398 G. R. CROTCH, M. A. 



Tribe 5. — Dytiscini. 



Thorax with the sides not margined, one posterior claw Cybister. 



Thorax not margined, posterior claws unequal. 



Scutellum none Lacco -hilns. 



Laciniae linear, episterna hardly reaching the coxa? Agabetes. 



Laciniae linear, dilated at apex. 

 Intermediate % tarsi simple. 



Coxae punctate Aril ius. 



Coxae smooth Therm on cetes. 



Intermediate tarsi dilated Grapboderes. 



Laciniai triangular. 



Surface smooth or finely punctulate 18 *, lint if us. 



Surface areolate Scutopterus. 



Surface transversly aciculate. 



% tarsi with discs beneath Colymbetes. 



% tarsi spongy beneath Cymatopterus. 



Thorax not margined, posterior claws equal Dytiscus. 



Thorax margined, claws unequal. 



Intermediate % claws unequal, laciniae triangular IShaiifus. 



Anal segment carinate in % IlybillS. 



Presternum sulcate. laciniae linear flatus. 



Thorax margined, claws equal. 

 Laciniae linear. 



Palpi emarginate, episterna not reaching the coxae Coptotomus. 



Elytra striate, episterna not reaching the coxae Copelatus. 



Elytra convex, very finely sculptured Ilybiosoilia. 



Antennae of male elavate Agabus. 



Laciniae sub-triangular. 



Thorax narrowed in front Gaurodytes. 



Thorax narrowed behind, legs long and narrow Anisomera. 



CY BISTER, Curt, Brit. Ent. (Type Roeselii.) 



Posterior tarsi with one claw only, two anterior tarsi in the male 

 forming a patella with equal rows of small cupulae, intermediate tarsi 

 compressed, claws unequal; metasternal laciniae abruptly curved, nar- 

 row, linear, dilated at the apex, not reaching the margin ; posterior 

 femora with apical angle not ciliate, tibiae short, apical margiu deeply 

 sinuate, tarsi elongate, last joint much larger than the fourth, coxal 

 plates widely divergent at the base, not reaching the metasternum. 



The stridulating organs in this genus have hitherto escaped notice 

 and are confined to the male sex ; they consist of 3--5 deep ridges in 

 the hollow behind the posterior coxae, and are rubbed by a ridge on 

 the underside of the femora. 



C fimbriolatus, Say, Am. Trans, ii., p. 91. — Ovate, above brown with a 

 faint green shade; thorax and elytra with a broad yellow margiD, the latter 



