ANATOMY AND TAXONOMY OF THE MATURE 
NAIADS OF THE DRAGONFLY GENUS 
PeEATHEMIS. (FAMILY LIBELLULIDAE)* 
By Harvey R. Levine 2 
Department of Entomology, University of Massachusetts, Amherst, Mass. 
The interrelationships of a particular group of insects cannot be 
fixed conclusively until a complete comparative study has been made. 
Studies of external morphology of various portions of widely differ- 
ing species of insects have been published, but detailed comparative 
studies, particularly on the generic and specific levels, are few. Not 
until one compares all the structures of any given species with all the 
structures of other species do we begin to understand fully the phylo- 
genetic and taxonomic relationships of the insects in question. 
The difficulty with which the immature stages of dragonflies are 
identified to species is concurrent with a sparsity of morphological 
work done on these naiads. This paper is intended to provide a de- 
tailed morphological study of the last instar naiad of a common 
dragonfly, Plathemis lydia (Drury), that may serve as a foundation 
for comparative morphological studies, which in turn may reveal some 
taxonomic characters. 
About 25 specimens were used in this study, and most of the fea- 
tures described were checked on the entire series. 
Figures of nearly all the external anatomical features of Plathemis 
lydia are included to supplement the discussion. The presentation of 
the comparative morphology of the mature naiad of the only other 
known species of this genus, Plathemis subornata Hagen, is supple- 
mented by figures wherever characters of taxonomic significance occur. 
EXTERNAL ANATOMY OF PLATHEMIS LYDIA (DRURY) 
The naiad of Plathemis lydia is rather large, robust, and elongate, 
approximately 23 to 24 mm. in length. Its surface is smooth and 
1 Contribution No. 1277 from the Department of Entomology, University of 
Massachusetts, Amherst, Mass. 
2The author wishes to express his sincere thanks and appreciation for the 
advice and criticism received from Dr. John F. Hanson and other staff members 
at the University of Massachusetts. He is also particularly indebted to Dr. R. E. 
Snodgrass for his valuable criticism of the manuscript. 
SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 134, NO. 11 
