THE PKEDACEOTJS DIVING BEETLES. 



211 



bh. Lower spur of hind tibiae dilated, much broader than the other ; front 

 tarsi of males as in Dytisclni; hind tarsi with one claw (males) or 

 very unequal claws (females) ; length 30 or more mm. 



Tribe IV. Cybistbini, p. 235. 



Tribe I. HYDROPORINI. 



Species of small size having the third joint of the front and 

 middle tarsi deeply lobed and concealing the fourth joint, which, 

 however, is often wanting ■ the fifth joint slender, with claws which 

 sometimes vary in form according to sex. The "elytra! ligula" 

 mentioned in the key is a tongue-like process on the inner face of 

 the side margin of the elytra, which must be lifted to show it. Its 

 function is to unite more perfectly the elytra and ventral segments. 

 Seven genera are probably represented in Indian a. 



KEY TO GENERA OF HYDEOPOBINI. 



a. Hind coxal cavities widely separated, each with an elongate notch be- 

 hind. IV. Hydeovatus. 

 aa. Hind coxal cavities not notched behind. 



ft. Size small, 1.5-2 mm. ; first ventral segment firmly united to border 

 of hind coxa?. 



c. Form rounded, convex ; prosternal process rhomboidal, acute at tip. 



V. Desmopachbia. 

 cc. Form oblong, depressed; prosternal process oblong. 



VI. Bidessus. 



hi). Size larger, 2.5 or more mm. ; first ventral segment free. 



d. Scutellum visible. VII. Celina. 

 dd. Scutellum not visible. 



e. Elytral ligula distinct, abrupt. VIII. Ccelambus. 



ee. Elytral ligula wanting. 



/. Mesosternum not reaching the metasternum. Debonectes. 

 ff. Fork of mesosternum connected with the intercoxal process of 

 the metasternum. IX. Hydbopobus. 



IV. Hydrovatus Mots. 1855. (Gr., ''water + old or stagnant.") 



This genus includes very small beetles which have the prester- 

 num dilated triangularly behind the front coxae and the tips of the 

 elytra produced into a sutural point. Two species are known from 

 Indiana. 



400 (1257). Hydrovatus pustulatus Melsh., Proc. Phil. Acad. Nat. Sci.. 

 II, 1844, 29. 



Form rounded, convex. Head, thorax (except basal cross-blotch) and 

 under parts reddish-yellow; elytra dark reddish-brown with a broad post- 

 basal and a narrow subapical cross-bar orange. Upper surface alutaceous ; 

 thorax faintly, elytra distinctly but sparsely, punctate. Length 2-2.5 mm. 



Northern two-thirds of State; frequent. May 15-August 20. 



