230 



FAMILY IV. DYTISCIDJE. 



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. 



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

 the outer margin. 

 6. Spurs of hind tibia? acute at apex ; claws of hind tarsi unequal. 



XX. Hydaticus. 



hi). Spurs of hind tibia? emarginate at apex. 



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



moderate sized punctures (male). XXL Aciljt/s. 



cc. Elytra not distinctly punctured, sometimes very finely punctulate 

 or partially acieulate. 

 d. Middle femora with long conspicuous seta?. 



XXII. Thermonectes. 

 dd. Middle femora with short, stout seta?. XXIII. Graphoderes. 



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

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



XTX. Dytiscus 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- 

 gate-oval, little eon- 

 vex and of variable 

 width ; elypeus 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 

 . sneeies alwavs have 



rig. llo. Dytiscm:— a, hrva of D. margmalis devouring a larva ot •>■ 

 En'aemera; b, pupa of same; c, D. fasciventris Say; grooved elytron of |i i j HpptVI v arir ] 

 it tarsus of male, under side, showing the suction cups; e, LliC L V lLcl UCC 1 J V o,llkx 



female; d, front 

 same of female. (After Riley.) 



broadly silicate 



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. 



