2? CONNECTICUT GEOL, AND NAT. HIST. SURVEY [Bull. 



always fused in Odonata, and the dividing line is traceable with 

 difficulty in adults. Except for the attachment of the second and 

 third pair of legs and the wings, there is little to separate them to 

 a casual observer. 



It is important to bear in mind that the thorax and abdomen of 

 all dragonflies are greatly modified and different in many respects 

 from other insects. There are, however, the usual "landmarks" 

 which facilitate a comparison of the sclerites in different groups. 

 In the thorax these consist of processes or points of articulation 

 of the appendages, particularly the legs, invaginations of the 

 internal skeleton, and breathing pores. 



The proximal segment of the legs, for instance, articulates with 



I ( Ante-clypeus 



Post-clypeus 



, Post-ocular spots 



=P°^5"^^=»>^-V-_Pre.ocular band 

 , Antenna 



Xv^ I ^// Compound eye 



^- — - -Occipital spinet 

 —Occipital horn 

 I ] L Tocellar ridge 



D I I .Occiput 



' Occipital ridge 



Fig. 3. Heads of Odonata from above, (a) Zygoptera, (b) Anisoptera 

 ( Ophiogomphus ) . 



the body in concave sockets that have lanceolate or somewhat 

 circular margins, with a lateral point or projection on each. The 

 point may be easily located by following the lateral ridge of the 

 coxa to the margin of the socket. Extending upwards from the 

 lateral points there is always a suture in the body wall of the 

 thorax which is important in separating the two sclerites, epi- 

 sternum and epimerum, of pro-, meso-, and metapleura. The 

 meso- and metepisterna are divided in Odonata into a dorsal divi- 

 sion (anepisternum)^ and a smaller ventral sclerite, the katepi- 

 sternum.* The notum of all thoracic segments except the first is 



'Formerly supraepisternum (see Comstock igao, p. si. for proper nomenclature). 

 * Formerly infraepisternum. 



