The Odonata of Canada and Alaska: Volume Three, Part III: The Anisoptera–Three Families 9781442654204

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THE ODONATA OF CANADA AND ALASKA

Edmund M. Walker (1877-1969)

The O D ON ATA of Canada and Alaska By EDMUND M. WALKER Professor Emeritus of Zoology, University of Toronto Honorary Curator of Zoology, Royal Ontario Museum

and P H I L I P S. C O R B E T Professor of Biology, University of Waterloo, Waterloo, Ontario VOLUME THREE PART I I I : THE ANISOPTERA

THREE FAMILIES

U N I V E R S I T Y OF TORONTO PRESS Toronto Buffalo London

© University of Toronto Press 1975 Toronto Buffalo London Reprinted, with corrections, 1978 Printed in Canada Library of Congress Cataloging in Publication Data Walker, Edmund Murton, 1877-1969. The Odonata of Canada and Alaska. Includes bibliographies. Vol. 3 by E. M. Walker and P. S. Corbet. CONTENTS: v. 1. General. The Zygoptera-damselflies. -v. 2. The Anisoptera-four families.-v. 3. The Anisoptera - three families. 1. Odonata-Canada. 2. Odonata - Alaska. I. Corbet, PhilipS. II. Title. QL520.2.C2W34 595.7'33'0971 54-4344 ISBN 0-8020-5321-1

FOREWORD In 1948 Professor Edmund M. Walker set out to assemble results of his fifty years' study of dragonflies into a faunistic monograph, The Odonata of Canada and Alaska. The first two volumes were completed and were published by the University of Toronto Press, in co-operation with the Royal Ontario Museum, in 1953 and 1958. Professor Walker was eventually forced by illness to give up his work on the third volume, and he died in 1969 at the age of 91. This book, with Professor Philip Corbet as co-author, is Volume III, the concluding part of the monograph. It was particularly heartening for Professor Walker, and for all of us concerned about the future of this large undertaking, when Professor Corbet agreed to accept responsibility for completion of Volume III. Through publication of many scientific papers on dragonflies, a book on the British species, and his well-known work A biology of dragonflies, Professor Corbet's background for the task was firmly established. His eligibility became complete when his professional career brought him to Canada, where he worked as a research scientist and later a research director with the Canada Department of Agriculture, before joining the staff of the University of Waterloo. Professor Walker's work on the monograph was supported by the Department of Entomology of the Royal Ontario Museum, where he was Honorary Curator, and where his collections are deposited. Professor Corbet's early work on Volume III was encouraged and facilitated by the Canada Department of Agriculture when he was a member of the staff, and his progress with the manuscript owes much to that support. At a later stage in the project, funds to engage assistants for technical and illustrative work were provided by a grant from the Canadian National Sportsmen's Show to the Department of Entomology, Royal Ontario Museum. This support came at a time when funds were not available elsewhere, and is gratefully acknowledged. The National Research Council of Canada and the Publications Fund of the University of Toronto Press made substantial grants towards the cost of publication. In bringing the monograph to completion with this volume, Professor Corbet has contributed a great deal of effort for which those concerned in any way with the biology of dragonflies are indebted to him. It is especially gratifying that the large task on which the last twenty years of Edmund Walker's life were concentrated is now complete. July 1973

GLENN B. WIGGINS Curator, Department of Entomology, Royal Ontario Museum

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PREFACE Professor Edmund M. Walker's accomplishments in the science and teaching of biology, which were both manifold and distinguished, have been reviewed in a specially prepared tribute volume (Wiggins, 1966). Of particular interest to students of the Odonata are the list of his publications, an autobiographical sketch (Walker, 1966a) and an account of his work on dragonflies (Corbet, 1966). The last of these items reveals clearly the measure of his contribution to our current knowledge of Canadian Odonata—a contribution covering a period of about seventy years and culminating in the monograph of which this is the third and final volume. When, in April 1964,1 accepted the invitation to complete Volume III of The Odonata of Canada and Alaska I did not expect that this task would take nearly as long as it has. Two circumstances have been largely responsible for this: first, the amount of work needed to revise and complete the manuscript was considerable, and required a familiarity with the North American dragonfly fauna that I did not at first possess; and second, the administrative responsibilities that I have assumed since 1967 have made it difficult to maintain the continuity of application needed for the prompt completion of such an undertaking. That this task is now finished is therefore largely due to the assistance that I have received and which it is a pleasure for me to acknowledge here. The financial resources needed for my work on this volume have come mainly from the Canada Department of Agriculture, as a consequence of my employment in its Research Branch until 1971, and the facilities that were so readily placed at my disposal there. Significant support has come also from the Department of Biology, University of Waterloo, and from a grant from the Canadian National Sportsmen's Show to the Royal Ontario Museum. I am glad of this opportunity to record my gratitude to the people who have given me valued assistance. My principal debt is to my wife, Dr. Hildegard Corbet, who has helped extensively with most aspects of the work. I thank Miss Barbara M. Rogers and Miss Patti Spry for thorough, accurate and expert assistance with the extraction and systematic presentation of source information, and Miss Rogers also for taking responsibility for the production of wing photographs, many of which were taken by Mr. P. Brian O'Donovan to whom my thanks are due. I am grateful to Mr. Marty Bueno de Mesquita and Miss Sally M. Melville for preparing most of the line drawings. Miss Jane Peterson has helped to prepare the index to this volume. For the provision of information and the loan of many specimens I am greatly indebted to Dr. Minter J. Westfall, Mr. J. E. H. Martin and Dr. Glenn

Vlll

PREFACE

B. Wiggins. I thank Dr. R.Jean Musser and Mr. Steve Jensen for the loan of the drawing reproduced in plate 39: 3, Drs. Dennis R. Paulson and Olavi Sotavalta for providing information, and Dr. George H. Bick, Dr. Jose I. Furtado, and Mr. Kenneth J. Deacon for commenting on parts of the text of this and previous volumes. As well as thanking persons mentioned in Volumes I and II, Dr. Walker and I wish to acknowledge the specimens or records received from Mr. Kenneth J. Deacon, Mr. William M. M. Edmonds, Dr. J. B. Falls, Dr. Jose I. Furtado, Mr. Alan Hayton, Miss Jane Peterson, Dr. Jean-Guy Pilon, Mr. Robert A. Restifo, Father J. C. E. Riotte, Dr. F. A. Urquhart and Dr. Harold B. White. Throughout this project I have greatly appreciated the encouragement that I have received from Miss Marjory A. Ford. Credits for the photographic illustrations are as follows: plates 2,7,20,22, 26 and 27 are from A manual of the dragonflies of North America (Anisoptera) by James G. Needham and Minter J. Westfall (1955), originally published by the University of California Press and reprinted here by permission of The Regents of the University of California; Mr. P. Brian O'Donovan took the photographs for plates 1, 4, 23, 24, 28 and 37. Credits for the line drawings are as follows, the convention "10:8" signifying "plate 10: figure 8": Mr. Marty Bueno de Mesquita for 3: 4, 5; 6: 3-7; 8: 1-12; 9: 1-12; 10: 1-7, 9-12; 11: 1-4, 7-13, 16; 12: 1-7; 13: 1-6; 14: 1-3, 5-7, 9; 21: 2, 3; 25: 1, 2, 5-9; 29: 1-4; 30: 4; 31: 14-16; 32: 1-6; 33: 1-3, 5; 34: 1, 3-7, 10; 35: 7; 36: 1-3, 5, 7; Miss Sally M. Melville for 3: 6, 7; 5: 1, 3, 5-8; 6: 1,2; 19: 1-7;21:7,8;30:3,6,7,9-14; 31: 1,2,4-8, 11; 36: 8-10; 38: 1-8; 39: 2; 42: 1-6; 43: 1-9; 44: 1-6; 45: 4-8; Dr. Hildegard Corbet for 10: 8; 11: 5,6,14,15; 13: 7; 14: 4,8; 21: 1,5,6; 25: 3,4; 29: 5; 30: 1,2,5,8; 31: 3,9, 10, 12, 13; 33: 4, 6; 34: 2, 8, 9, 11, 12; 35: 1-6, 8; 36: 4, 6; 45: 1-3; Dr. E. M. Walker for 3: 1-3; 5: 2, 4, 9, 10; 21: 4; 39: I; 40: 1-4; 41: 1-6. In the fifteen years that have elapsed since the publication of Volume II there have been several developments of interest to students of Canadian Odonata. Three years ago White and Raff (1970) discovered the nymph (larva) of Williamsonia lintneri (Hagen); thus there is now no genus of the Canadian dragonfly fauna that remains unknown in the nymphal stage. Remaining to be found and described is the nymph of the only Canadian species of Williamsonia: W. fletcheri Williamson—a prize for some fortunate collector! Other recent work which we may hope will soon be extended to involve Canadian species and populations is that on adult behaviour (e.g. Bick and Bick, 1961, 1963; Johnson, 1962a, 1962b) and on the responses of nymphs to day-length and temperature that regulate the timing of seasonal emergence (e.g. Lutz and Jenner, 1964; Lutz, 1968). Four species have been added to the Canadian list, and the known distribution of many Canadian species has been extended (such information has been included in the Addenda to Volumes I and II on p. 279).

PREFACE

IX

Another noteworthy development that we have witnessed, and one with fundamental implications, is the rapidly growing human pressure on land in the southern region of Canada. Because of the progressive and usually irreversible habitat destruction it entails, this offers as a prospect in the years to come a significant diminution of the Canadian dragonfly fauna. This process will probably become evident first in southwestern Ontario, which contains more species of dragonfly than any comparable area in Canada and is also subject to the greatest pressures from agricultural, industrial and urban growth. When this growth stops—as eventually it must—it is to be hoped that the remaining freshwater habitats will still sustain a diverse and vigorous dragonfly fauna—a reliable, and delightful, indicator of a healthy environment. July 1973

P.S.C.

Readers who wish to correspond with the second author should note that in May 1974 his address became: Department of Zoology, University of Canterbury, Christchurch, New Zealand.

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ABBREVIATIONS Defined below are abbreviations appearing in the text. Abbreviations used in any plate are denned in the caption to that plate. Those used for measurements (of adults or nymphs) have a precise meaning that is specified in the appropriate section of the Introduction. GENERAL inf.—inferior abd.—abdomen, abdominal lat.—lateral ale.—in alcohol ant.—anterior mm.—millimetres anx—antenodal cross-veins Mt(s).—Mountain(s) N.—north latitude app(s).—appendage(s) n.—north E.—east longitude pnx—postnodal cross-veins e.—east excl.—excluding Pt.—Point exuv.—exuvia, exuviae pt.—pterostigma, pterostigmata f.w.—fore wing Rlwy.—Railway Ft.—Fort s.—south hd.—head seg(s).—segment(s) h.f.—hind femur spt.—supratriangle h.w.—hind wing, hind wing-sheath vs.—versus I(s).—Island(s) W.—west longitude w.—west or width in lift.—by letter incl.—including PROVINCES Alta.—Alberta B.C.—British Columbia Labr.—Newfoundland (Labrador) Man.—Manitoba Nfld.—Newfoundland (Island) N.B.—New Brunswick

OF CANADA N.S.—Nova Scotia Ont.—Ontario P.E.I.—Prince Edward Island Que.—Quebec Sask.—Saskatchewan

TERRITORIES OF CANADA N.W.T.—Northwest Territories Yukon T.—Yukon Territory

Xll

ABBREVIATIONS

STATES OF UNITED STATES (states not listed here are not abbreviated) Ala.—Alabama Nebr.—Nebraska Ariz.—Arizona Nev.—Nevada Ark.—Arkansas N.H.—New Hampshire Calif.—California NJ.—New Jersey Colo.—Colorado N.Mex.—New Mexico Conn.—Connecticut N.Y.—New York Del.—Delaware N.C.—North Carolina D.C.—District of Columbia N.Dak.—North Dakota Fla.—Florida Okla.—Oklahoma Ga.—Georgia Oreg.—Oregon 111.—Illinois Pa.—Pennsylvania Ind.—Indiana R.I.—Rhode Island Kans.—Kansas S.C.—South Carolina Ky.—Kentucky S.Dak.—South Dakota La.—Louisiana Tenn.—Tennessee Me.—Maine Tex.—Texas Md.—Maryland Vt.—Vermont Mass.—Massachusetts Va.—Virginia Mich.—Michigan Wash.—Washington Minn.—Minnesota W. Va.—West Virginia Miss.—Mississippi Wis.—Wisconsin Mo.—Missouri Wyo.—Wyoming Mont.—Montana

CONTENTS FOREWORD BY DR. GLENN B. WIGGINS

v

PREFACE

vii

ABBREVIATIONS

xi

PART III. THE ANISOPTERA OF CANADA AND ALASKA (continued) INTRODUCTION SUPERFAMILY LIBELLULOIDEA TILL YARD

Key to the Families of Libelluloidea

FAMILY MACROMIIDAE

Key to the Genera of Macromiidae Genus Didymops Rambur Didymops transversa (Say) Genus Macromia Rambur Key to the Species of Macromia Macromia illinoiensis Walsh Macromia magnifica MacLachlan Macromia rickeri Walker

FAMILY CORDULIIDAE

Key to the Genera of Corduliidae Genus Neurocordulia Selys Neurocordulia yamaskanensis (Provancher) Genus Epitheca Burmeister Key to the Species of Epitheca Epitheca princeps Hagen Epitheca cynosura (Say) Epitheca spinigera (Selys) Epitheca canis MacLachlan Genus Helocordulia Needham Helocordulia uhleri Selys Genus Williamsonia Davis WiUiamsoniafletcheri Williamson Genus Somatochlora Selys Key to the Species of Somatochlora Somatochlora walshii (Scudder) Somatochlora minor Calvert Somatochlora elongata (Scudder)

1 3 12

15 16

19 19 20 22 23 23 27 30 33

34 36 37 39 41 42 45 51 54 57 59 62 63 65 67 74 78 82

XIV

CONTENTS

Somatochlora williamsoni Walker Somatochlora ensigera Martin Somatochlora tenebrosa (Say) Somatochlorafranklini (Selys) Somatochlora kennedyi Walker Somatochlora forcipata (Scudder) Somatochlora incurvata Walker Somatochlora semicircularis (Selys) Somatochlora whitehousei Walker Somatochlora septentrionalis (Hagen) Somatochlora sahlbergi Trybom Somatochlora albicincta (Burmeister) Somatochlora brevicincta Robert Somatochlora hudsonica (Selys) Somatochlora cingulata (Selys) Genus Cordulia Leach Cordulia shurtleffi Scudder Genus Dorocordulia Needham Key to the Species of Dorocordulia Dorocordulia libera (Selys) Dorocordulia lepida (Hagen) FAMILY LIBELLULIDAE

Key to the Genera of Libellulidae Genus Nannothemis Brauer Nannothemis bella (Uhler) Genus Perithemis Hagen Perithemis tenera (Say) Genus Celithemis Hagen Key to the Species of Celithemis Celithemis eponina (Drury) Celithemis elisa (Hagen) Celithemis monomelaena Williamson Celithemis martha Williamson Genus Libellula Linne Key to the Species of Libellula Libellula quadrimaculata Linne Libellula julia Uhler Libellula exusta Say Libellula lydia Drury Libellula luctuosa Burmeister Libellulaforensis Hagen Libellula pulchella Drury Libellula semifasciata Burmeister

84 88 90 94 98 101 104 106 110 113 116 119 125 126 130 133 135 137 139 140 142 144

145 147 149 151 152 154 155 156 158 160 161 162 164 165 169 172 173 175 178 179 183

CONTENTS

Libellula incesta Hagen Libellula vibrans Fabricius Genus Erythemis Hagen Erythemis collocata (Hagen) Erythemis simplicicollis (Say) Genus Pachydiplax Brauer Pachydiplax longipennis (Burmeister) Genus Erythrodiplax Brauer Erythrodiplax berenice (Drury) Genus Sympetrum Newman Key to the Species of Sympetrum Section 1 Sympetrum corruptum (Hagen) Sympetrum illotum (Hagen) Sympetrum madidum (Hagen) Section 2 Sympetrum vicinum (Hagen) Sympetrum costiferum (Hagen) Sympetrum semicinctum (Say) Sympetrum occidental Bartenev Sympetrum danae Sulzer Section 3 Sympetrum ambiguum (Rambur) Sympetrum rubicundulum (Say) Sympetrum internum Montgomery Sympetrum obtrusum (Hagen) Sympetrumpallipes (Hagen) Genus Leucorrhinia Brittinger Key to the Species of Leucorrhinia Leucorrhinia borealis Hagen Leucorrhinia hudsonica (Selys) Leucorrhinia patricia Walker Leucorrhinia glacialis Hagen Leucorrhiniaproxima Calvert Leucorrhiniafrigida Hagen Leucorrhinia intacta Hagen Genus Tramea Hagen Key to the Species of Tramea Tramea Carolina (Linne) Tramea lacerata Hagen Tramea onusta Hagen Genus Pantala Hagen Key to the Species of Pantala Pantala hymenea (Say) Pantalaflavescens (Fabricius)

XV

185 187 190 190 191 193 193 196 196 198 202 205 205 209 211 213 213 215 219 220 222 226 226 227 230 232 234 236 237 240 244 246 249 251 255 257 261 262 262 265 268 271 273 273 275

XVI

CONTENTS

ADDENDA AND CORRIGENDA: VOLUMES I AND II

279

BIBLIOGRAPHY

287

SUBJECT INDEX

301

AUTHOR INDEX

303

ODONATAINDEX

305

PART III (continued)

THE ANISOPTERA OF CANADA AND ALASKA

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INTRODUCTION The two preceding volumes of this monograph deal, respectively, with the Zygoptera (Walker, 1953) and with four families of the Anisoptera: the Aeshnidae, Petaluridae, Gomphidae and Cordulegastridae (Walker, 1958). Volume III deals with the superfamily Libelluloidea of the Anisoptera, which encompasses three families: the Macromiidae, Corduliidae and Libellulidae. The known Canadian representatives of these three families comprise 77 species belonging to 20 genera. At the time that this volume went to press the species of Odonata that had been recorded from Canada (including the additions listed on p. 279) amounted to 194, of which 51 are Zygoptera. The contents of Volume III are arranged and treated almost exactly as in Volume I and II. To comply with the first author's intention regarding this volume and to conform with his practice in preceding volumes, species have been listed in the order that reflects Walker's assessment of their affinity. So that descriptions of given species can be located readily, I have made liberal use of page references in the text. In the rest of this introduction I describe the procedures followed, and define the terms employed in each part of the text so as to reduce the likelihood of misunderstanding or imprecision when the descriptions are being used. So far as is possible, remarks are placed in the same sequence and under the same headings as will be found in the text. Abbreviations of terms used generally in the text are defined on page xi; those limited to particular sections are defined or referred to below. Use of the pronoun "I" in the Preface and Introduction signifies a statement by the second author alone; if used elsewhere in the text its authorship will be evident from the context. Use of the pronoun "we" signifies an observation by both or either of the authors (but usually by the first author alone), thus preserving a usage adopted in Walker's previous publications. SUPERFAMILY, FAMILIES AND GENERA The superfamily Libelluloidea and each family and genus are prefaced by a section describing the principal distinguishing features of each, first of adults and then of nymphs. This section is normally short but is most detailed for the three genera that are primarily north-temperate in distribution and that are therefore particularly strongly represented in Canada and Alaska, namely Somatochlora, Sympetrum and Leucorrhinia. Amplifying statements regarding keys to species, which appear below, apply equally to keys to families and genera.

4 Adult

THE ODONATA OF CANADA AND ALASKA

SPECIES

Keys and descriptions. The attributes used in the adult keys have been derived from a wide variety of sources, including the authors' own observations. For this reason, and because several sources sometimes contribute to a single couplet, it is impracticable to cite or identify the original authorship of a diagnostic character. However, it is appropriate here to mention the books by Needham and Westfall (1955) and Robert (1963) which were used most frequently, the key by Borror (1945) for Libellulidae, and that by Gloyd (1958) which was adopted without change for Tramea. The other publications used are listed in the Bibliography but not necessarily cited elsewhere in the text. Where restrictions govern the use of a key, these are mentioned in the preamble to that key. General morphological terms have been defined in Volume I (pp. 4-23), or, if convenience requires this, by an illustration in this volume cited in the relevant couplet of a key (see plates 21, 29, 30, 35 on pp. 138, 208, 212,242). Terms used for venation are not those used in Volume I, which follows the Comstock-Needham system. In Volumes II and III the Tillyard-Fraser system has been adopted (see remarks below under Venation). In the keys the abbreviations given for measurements are those defined below under Measurements. Use of such an abbreviation signifies that the numerical value given is a dimension. Whenever segments are mentioned without further qualification, these are abdominal segments. The purpose of the species descriptions is to amplify and supplement the diagnostic characters given in the keys and illustrations. The descriptions vary in content, length and detail according to the species and the ease with which it can be identified. For some genera of Libellulidae that are not well represented in Canada and Alaska it has sometimes proved difficult to obtain adequate material for examination; in such cases use has been made, to a varying degree, of published descriptions, particularly by Needham and Westfall (1955) but also by Carman (1927), Byers (1930) and other authors. Venation. Entries that I have had to provide have been derived, where possible, from five or more specimens, and by preference from Canadian material. It had been the first author's manifest intention to use the system of Tillyard and Fraser (1957) in this volume, as evidenced by the completed parts of the text and by his remarks in Volume II on pages vii and 5-9. To make it easier for the reader to relate the Tillyard-Fraser system to that used by Comstock, Needham, Westfall and others, the first author illustrated the salient features of each in plate 8 on p. 70 in Volume II.* However, since it is *"Cu2" in the upper figure of this plate should be "CuP."

INTRODUCTION

5

necessary to illustrate certain venational characters of the Libelluloidea in Volume III in any case, the opportunity has been taken to include a complete list, with illustrations and abbreviations, of the terms used in this volume (pi. 1, p. 6), and also a list of the main terms that differ in the two systems. Readers who require further information on venation should consult Volume I (pp. 10-17) and Volume II (pp. 5-9, 70,71). Excellent illustrations devoted to special features of venation are given by Needham and Westfall (1955) on pp. 20, 63, 347 and 423-425. The numbers of antenodal and postnodal cross-veins (anx and pnx) are expressed as ranges (with occasional or less common values given in parentheses) with counts for the two wings being given in the form "fore wing/hind wing." Fractional values (e.g. in Erythrodiplax and certain Sympetrum) denote the existence of an incomplete cross-vein, at the distal end of the first series. An incomplete antenodal cross-vein is typically present in this position in the fore wing ofPantala and Tramea; however, the frequent lack of correspondence between the cross-veins of the first and second series in these genera renders fractional values less informative than in other genera. Therefore in Pantala and Tramea the values given for anx refer only to those in the first series (e.g. 1 IVz for a genus like Sympetrum [expressed here as " 11.5"] would be recorded as 12 for Tramea). An entry in the form "(NW: 6* 9 hind wing 5-6)" indicates that the range given by Needham and Westfall (1955) extends beyond the smallest or greatest values for the specimens on which the counts for this volume were based. Measurements. Unless obviously incorrect (e.g. because of a transcription error) the values in the first author's original manuscript have been included without alteration. None of the first author's fractional values have been rounded to integers, since he alone was aware of the precision that accompanied his original measurements. Measurements that I have had to provide have been derived, where possible, from five or more specimens, and by preference from Canadian material; and they have been made to the nearest 0.1 millimetre. With negligible exceptions the same measurements are provided for all species within a genus, though they may differ for species from different genera. If the range for the length of the hind wing (h.w.) given by Needham and Westfall (1955) extends beyond the smallest or greatest dimensions for specimens treated here by more than 0.5 millimetre, the range is given after our entry in the form "(NW: 6* 2 10-15)." In the few (seven) other cases where measurements are provided from, or qualified by, values from other sources, these are identified by an asterisk for which an explanation is provided at the end of the paragraph. The abbreviations used for measurements are defined as follows: Total length: the distance between the anterior surface of the head (excluding the antennae) and the posterior margin of

PLATE 1

1

2 PLATE 1

The principal venational characters of the Libelluloidea according to the Tillyard-Fraser system, which is used in this volume: (1) Cardulia shurtleffi, fore and hind wings; (2) Erythemis simplicicollis, base of hind wing showing venation in the expanded anal region characteristic of the Libellulidae; a dotted line indicates the margins of the anal loop.

INTRODUCTION

7

abdominal segment 10 (that is, excluding the anal appendages or ovipositor). Length of abdomen (abd.): the distance between the anterior margin of segment 1 and the posterior margin of segment 10 (that is, excluding the anal appendages or ovipositor). Width of abdomen (w.abd.): the greatest width. Length of hind wing (h.w.): the distance between the sclerotized basal hinge (at its point of articulation) and the apex of the wing. Length of hind femur (h.f.): the distance between proximal and distal ends (coxa and trochanter excluded). Width of head (w.hd.): the greatest width. Length of pterostigma (pt.): the greatest length, measured along the costal margin of the wing (that is, not along the diagonal of the pterostigma); where applicable, an oblique stroke divides the entries for fore and hind wings; the absence of such division implies that values apply to both wings. When using these measurements it is important to remember that they should be considered only as a guide to the identity of specimens but (unless mentioned as such in the key) not as diagnostic criteria. When comparisons are being made with measurements given by other authors the way the measurements are defined should be carefully noted: unlike Walker (see

Abbreviations (Equivalent notations in the Comstock-Needham system are included in parentheses where the two systems differ.) 1A—analvein (Cu2> N—nodus a—ankle cell pnx—postnodal cross-veins, first or anterior aa—anal angle series ac—anal crossing pr—paranal cells al—anal loop pst—post-trigonal cells anx—antenodal cross-veins, first or anterior pt—pterostigma series Ri—branch of radius (R) arc—arculus R 2 —branch of radius (Mi) at—anal triangle R3—branch of radius (M 2 ) b—bridge R-i+s—branch of radius (Ma) bv—brace vein r—reverse vein C—costal vein Rspl—radial supplement or planate CuP—cubital vein or posterior cubitus (Cm) s—subtriangle g—gaff Sc—subcostal vein h—heel cell si—sole IR2—radial intercalary vein (M1A) sn—subnodus IRa—radial intercalary vein (Rs) spt—supratriangle or supertriangle MA—anterior media (M