No. 39] 



ODONATA OF CONNECTICUT 



21 



mobility. It varies in form in different families and is important 

 in classification. 



Thorax. — The thorax is composed of four rings or body seg- 

 ments. Immediately behind the head is the microthorax, a very 

 small incomplete ring composed of a small plate on either side. 

 Following this is the prothorax, a larger segment, to which is 

 attached the first pair of legs. The region of the prothorax, or 

 in fact all parts of the thorax above, on either side, and below, 

 may be known in a general way as notum, pleura (singular, 

 pleurum) and sternum. The caudal margin of the pronotum is 





Fig. 2. Adult Anisopteron {Anax Junius) showing parts. 



usually provided with a thin transverse edge frequently project- 

 ing dorsad — a variable feature of use in classification. The pleura 

 are divided into two sclerites by a line extending dorsad from the 

 lateral articulations of the coxae or segment of the legs next the 

 body. There is also a suture separating notum from pleura, but 

 it is often obscure. None of the sclerites of the prothorax are of 

 much taxonomic value except the pronotum. 



The mesothorax and metathorax- (following the prothorax) are 



* Sometimes called synthorax (Tillyard 1917, p. 22). 



