DYTISCIDAE. 63 



Hind coxffi longer near the middle of the body ; (prosternum dilated behind, 

 truncate or nearly so.) Nothhim. 



Hind coxa; longer near the sides of the body ; (prosternal process com- 

 pressed, attaining the mctasternum.) LACCoi'niLiNi. 



These species are all of suiall size ; the Notevini are convex, 

 obtuse ill front, pointed behind ; the Laccophilini are less con- 

 vex, and of the average form of Dytiscidie. 



Tribe 1.— ]\OTERII¥I. 



Prosternum flat, gradually and convexly flexed in front. 2. 



Prosternum sulcate, jjerpendicular in front. Colpius. 



2. Last joint of maxillary palpi emarginate ; hind tibia^ less dilated, pro- 



steinal process not broader tlian long. Canthydrus. 



Last joint of maxillary palj^i truncate, hind til)i;p bi-oadcr ; pinsternn! 



process very broad. Hydrocanthus. 



Last joint of palpi rounded at tip; prosternal process rounded ; meta- 



sternum and hind coxfe connate (size very suiall). Notomicrus. 



The species of the second genus, recently established by Sharp, 

 are those referred to Suphis in our catalogues, from vvliich they 

 differ by the hind femora nt base being contiguous. Nolomicru^ is 

 represented in our fauna by N. tiatndus (Loc.) from Louisiana. 

 None of this tribe have yet occurred in the J'acific region. 



Tribe II.— LACCOPIIII.I.\I. 



A nioderute number of species of Laecophilus, usually spotted, 

 and sometimes so clo.sely allied as to be with difficulty distin- 

 guished, represent this tribe in all parts of our country. One of 

 the best characters is that developed by Crotch, which depends 

 on the number of |)arallel ridges seen on the hind coxa) of the %, 

 beginning near the middle at the insertion of the femora, and ex- 

 tending outwards and backwards. These ridges, with their fde- 

 like arrangement, constitute a stridulating organ. 



Series IT. — Pytiscid/K complicati. 



The great bulk of the species of the family belong to this series, 

 which differs from all other Coleoptera, except Mormolyco and 

 Amphizoa, by the middle coxa! cavity inclosed by foio- distinct 

 pieces, in consequence of the episterna of the metasternwni enter- 



