JOURNAL 



JMj JBorfe €SnfomologirflI %m\tty. 



Vol. XIII. SEPTEMBER, 1905. No. 3 



Class I, HEXAPODA. 



Order II, COLEOPTERA. 



THE DISTINCTIVE CHARACTERS OF THE EAST- 

 ERN SPECIES OF THE GENERA DYTISCUS 

 AND CYBISTER. 



By C. H. Roberts,. Sc.D., 

 New York, X. Y. 



All the species of the genus Dyliscus are of large size, the upper 

 surface of dark color with a yellow stripe along the side of the thorax 

 and elytra ; the clypeus is yellow, and there is on the middle of the 

 head an angular yellow mark ; in addition to these yellow marks some 

 species have the anterior and posterior margins of the thorax yellow, 

 and the eyes margined with yellow. The color of the under surface 

 is either pitchy black or yellow, or is intermediate between the two, 

 or a mixture of them. 



The form is comparatively little convex, always elongate, but ot 

 variable width. 



The clypeus is always separated from the head by a suture visible 

 across the whole width of the head. This entire clypeal suture, so 

 far as has been observed, exists only in this genus and in the European 

 genus Meladema in the Dytiscidas, although it occurs in Pelobius and 

 Amfi/iizoa, and is common in the Carabidae. The prothorax is desti- 

 tute of a lateral margin. The prosternal process is of variable length, 

 rather elongate and narrow, distinctly margined at the sides and is 

 received into a groove of the metasternum. 



The hind legs are but little developed for swimming being long 



103 



