904 On Aquatic Caimivorous Coleoptera or DytisciJoB. 



The swimming legs and hind coxse are quite as well developed as they are in the 

 most perfect species of Dytiscus. The form of the coxal lines and processes is very 

 similar to that of Dytiscus hybridus. 



We find in Hyderodes, as in Dytiscus, dimorphic females ; certain individuals 

 of that sex beinc smooth like the males, while others have the thorax and elytra 

 rouo-hened, by a peculiar, very coarse and deep, irregular sculpture, giving rise to 

 a corroded ajjpearance. 



I. 66. -Genus DYTISCUS. {Vide p. 634.) 

 All the species forming this aggregate (twenty-two in number) are of lartre size, 

 (an inch or an inch and a half long), the upper surface is of dark colour with a 

 yellow stripe along the side of the thorax and elytra, the clypeus is yellow, and there 

 is on the middle of the head an angular yellow mark ; in addition to these yellow 

 marks some species have the anterior and posterior margins of the thorax } ellow, 

 and the eyes margined with yellowish colour. The colour of the under surface is 

 either pitchy black or yellow, or is intermediate between the two colours, or a 

 mixture of them. The form is comparatively little convex, always elongate, but of 

 variable width. 



The clypeus is always separated from the front of the head by a suture visible 

 across the whole width of the head. The prothorax is destitute of a lateral margin. 

 The prosternal process is of variable length, usually rather elongate and narrow, 

 being only very little widened out after passing the coxse, it is not compressed, and 

 is indistinctly margined at the sides, the margin not extending to the extremity ; 

 in a few species the process is short and comparatively little acuminate {e.g., D. 

 latissimus, and D. lapponicus). The inter-coxal process of the metasternum is 

 occupied by an elongate narrow depression for the reception of the prosternal 

 process. The hind legs are but little developed for swimming, being elongate and 

 rather slender ; the femur has a group of accumulated setigerous punctures at the 

 extremity that does not quite extend to the hind margin ; their tibije are usually 

 about three times as long as they are broad ; the tarsi are considerably longer than 

 the tibia), and are terminated by two rather slender, curved, nearly equal claws, thci 

 hind margins of their joints are but little lobed externally. In the more perfect 

 species {e.g., D. hybridus, and habilis) the swimming legs have become shorter and 

 thicker, and their claws more unequal. 



The hind coxas are rather small, and their anterior border is not much arched, 

 the wings of the metasternum are only of moderate area. The coxal lines are but 

 little bent, and the coxal lobes have a great extension in the longitudinal direction, 

 while they are comparatively small in the transverse direction ; the coxal border is 

 elongate, and before the apex is usually a good deal broader than in front, the 

 coxal notch is elongate, and beyond it the processes tend, in numerous species, to 

 lengthen and become slender, so as to form two spinose projections in the extreme 



