On Aquatic Carnivorous Coleoptera or Dytiscidce. 905 



cases. The abdominal stigmata are large, the terminal two being very much 

 larger than the othei's and very highly developed. 



The anterior tarsi of the male are very highly developed; the three basal joints 

 are very dilated, and coadapted to form a nearly circular saucer, this is fringed at 

 the circumference beneath with elongate hairs, and their under surface bears two 

 large palettes at the base, and elsewhere a dense glandular pubescence, each hair of 

 which is in fact a stalk bearing a minute palette at the extremity ; the fourth and 

 fifth joints are not dilated, the latter is elongate. The middle tarsi of the male 

 have the three basal joints dilated and elongate, the three together thus 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 second bears deep elongate grooves on the 

 winof-cases. 



The species inhabit the northern parts of the Old and New Worlds ; Persia and 

 Japan are the extreme points to which it extends, each of these countries possessing 

 one peculiar species. 



The genus is remarkable by the entire clypeal suture ; this character, so far as I 

 have observed, exists only in this genus, and in Pelobius and Amphizoa, and in 

 Meladema of the Colymbetides,and is found in no other Dytiscidai, although it is com- 

 mon in Carabidte ; — in Harpalus caliginosus, for example, it is very similar to what it 

 is in Dytiscus. The suture however varies greatly in its depth in different species 

 of the genus, and differs, in certain species, greatly in the two sexes ; thus in D. 

 hybridus and D. habilis it is very obliterated, while it is very distinct in D. cir- 

 cumflexus, and D. dauricus, and in the latter species is in the female so distinct 

 that the clypeus is conspicuously i-aised or swollen. 



Certain species may be considered as more perfect, or higher, than others of the 

 genus; thus D. habilis and D. hybridus have the form continuous and perfect, as in 

 all the higher water beetles, and the swimming legs more abbreviated and thickened ; 

 these species have the coxal processes rounded ; in others of the genus the form is 

 very discontinuous, and in these species the coxal processes are very spinose ; 

 should these characters continue to be differentiated, the genus will clearly 

 become divisible into two or more aggregates when the various forms become more 

 perfected. 



Dytiscus latissimus is most remarkable by the great develojiment of its surface 

 which is increased by the great expansion of the elytral and thoracic margins ; it 

 is worthy of remark that this species is very subject to deformities, and its breast 

 is marked by wrinkles (w-hich occasionally are quite deep) as if the surface were 

 subject to some kind of tension : in one specimen in my collection the whole of the 

 middle portion of the metasternum is thrown into concentric wrinkles, and the 

 .strain has so affected the structure that the inter-coxal process of the metasternum 



