10t Journal New York Entomological Society. [Vol. xm. 



and rather slender. Their tibia; are usually about three times as long 

 as broad ; the tarsi are considerably longer than the tibiae and are 

 terminated by two rather slender, curved, nearly equal claws. In the 

 more perfect species, as hybridus, the swimming legs have become 

 shorter and thicker and their claws more unequal. 



The hind coxae are rather small and the wings of the metasternum 

 of moderate area ; the coxal notch is elongate, and beyond it the 

 coxal processes tend, in numerous species, to lengthen and become 

 slender, so as to form two spinous projections in the extreme cases. 



The anterior tarsi of the male are very highly developed ; the 

 three basal joints are very much dilated and form a nearly circular 

 saucer, fringed at the edges beneath with elongate hairs, and bearing 

 on their under surface two large palettes at the base, and elsewhere a 

 dense pubescence — each hair bearing a minute palette at its ex- 

 tremity ; the fourth and fifth joints are not dilated, the latter elongate. 



The middle tarsi of the male have the three basal joints dilated 

 and elongated, the three together assuming a narrow, parallel form, 

 and are densely clothed beneath with a glandular or spongy pubescence. 



In many species the females are dimorphic, one form being nearly 

 similar to the male in sculpture, while the other bears deep elongate 

 grooves on the elytra. 



The species of Dytiscus inhabit the northern parts of the new and 

 old worlds, and Persia and Japan have each one peculiar species. 



The species of Cybister are also of large size and there are 

 numerous species scattered over the whole world. They differ from 

 Dytiscus in that the males have only a single claw on the hind tarsus ; 

 the females also usually have only one, and in certain cases a rudi- 

 mentary second on the underside at the inner edge of the larger one. 

 The presternum is not channelled. 



We have but one eastern species. 



Dr. D. Sharp has separated Dytiscus into four groups as follows: 



Group I. — Labrum distinctly etnarginate in middle; apices of 

 coxal processes not spinose. Into this groups fall our species fasci- 

 ventris, hybridus, verticalis, marginicollis, sublimbatus and marginalis. 

 Of these we have in the East fasciventris, hybridus, verticalis and 

 perhaps marginalis. 



Group II. — -Labrum distinctly emarginate in middle; apices of 

 coxal processes acutely spinose. Into this group fall circumcinctus, 

 parvulus, vexatus and dauricus. 



