230 



FAMILY I V. DYTISCITXE. 



KEY TO INDIANA GENERA OF DYTISCINI. 



a. Length one inch or more; joints of hind tarsi not fringed with flattened 

 hairs on the outer margin, the last one with two claws; front tarsi 

 of males with two large and numerous small disks. 



XIX. DYTISCUS. 

 mi. Length scarcely exceeding one-half inch ; joints of hind tarsi fringed on 



the outer margin. 

 6. Spurs of hind tibhe acute at apex : claws of hind tarsi unequal. 



XX. HYDATicrs. 

 ljl>. Spurs of hind til)i;e emarginate at apex. 



c. Elytra either 4-sulcate (female), or with distinct, closely placed. 



moderate sized punctures (male). XXI. Acn.n's. 



cc. Elytra not distinctly punctured, sometimes very finely punctulate 



or partially aciculate. 

 </. Middle femora with long conspicuous seta 1 . 



XXII. THERMONEOT.S. 

 ild. Middle femora with short, stout seta?. XXIII. GRAPHODER[:S. 



The emarginate or bifid tips of the tibial spurs in the last throe 

 genera are very fine, and must he looked for with a good lens. 



XIX. Dvnsrrs Linn. 1735. (Gr., "a diver.") 



To this genus belong the largest of our diving beetles. They 

 are of a dark olive-brownish hue. with the elypeus and a stripe 

 along the sides of thorax and elytra dull yellow; front and hind 



margins o f thorax 

 also usually more or 

 less yellow. (Fig. 

 115.) Form elon- 

 .uale-oval, little con- 

 vex and of variable 

 width; clypeus sepa- 

 rated from head by 

 a suture visible 

 across the full width 

 of head; thorax not 

 margined; claws 

 equal in both sexes. 

 The females of some 



Fig. 115. Dytiscin: ,1, larva of D. marginalia devouring a larva of *P^ 



Epheuiera; b, pupi of s.une; c, D. fasciventris Ray; grooved elytron of j.i plvtvi flf>pi-dv nnrl 

 fein lie; </, front tarsus of male, under side, showing the suction cups; e, . l l 1 . <" 



same of female. (After Rilev.) in 



broadly sulcate; i n 



some they are always smooth, while in a third group the females 

 are dimorphic, i. e., have either smooth or sulcate elytra. Four 

 species are known from Indiana, while three others perhaps occur. 



