DYTISCIDAE. 



Hd 



The olytral ligula is ii tongue-like process on the inner face of 

 the side margin of tlie elytra, for the purpose of making the union 

 between the elytra and the ventral segments more perfect. 



The genera are represented on both sides of the continent, but 

 the species are far more numerous in the northern than the 

 southern parts. ISeveral species seem to be common to the two 

 continents. 



Tribe II.— COLYMBETIi\I. 



Two groups have been detined by Dr. Sharp, as follows: — 



Semimembranous side piece of 1st dorsal segment smootli. Agabi. 



Semimembranous side piece of 1st dorsal segment rugose. Colymbetes. 



Group I. — Agabi. 



The species are of moderate size, and like those of the follow- 

 ing group have the setigerous punctures of tlie hind femur either 

 conspicuous or absent. Dr. Sharp has, in our opinion, given to 

 this character an undue significance, unworthy of group distinc- 

 tion. As tile corrugation of the membranous portion of tlie first 

 dorsal segment near the spiracle seems to us more important than 

 the presence or absence of the femoral setigerous punctures, we 

 have placed in this group some of the unassociated genera of Dr. 

 Siiarp, Copelates, Matus, and Agabetes, and we think that we 

 see in thein closer alliances to the genera with which we have 

 associated them, than can be found elsewhere in our fauna. 



The genera are as follows: — 



Hind tarsi with equal claws. 2. 



Hind tarsi with unequal claws; joints lobed on tin; outrr inferior edge : 



elytra with a pubescent spot on the inner face at the npcx. Ilybiiis. 



2. Last joint of palpi normal, not dilated. :j. 



Last joint of jjalpi emarginate. Coptotomus. 



Last joint of palpi dilated. Hydrotrupes. 



.S. Wing of metasternum wedge-shaped, not linear. ;'). 



Wing of metasternum linear, deflexed outwardly. 4. 



Hind legs short and stout ; elytra not striate. Ilybiosoma. 



Hind legs slender ; elytra striate. Copelatus. 



4. ('oxal lines fine, sinuate. ;'>. 



Coxal lines deep, and n(!arly straight, Agabinus. 



'). I'rosternum not suh-ate. ti. 



Prosternum sulcate. Matns. 



f). Prothorax not margined. Agabetes. 



Prothorax margined at tlie sides. Agabua 

 5 



