On Aquatic Carnivorous Coleoptera or Dytiscide. 905 
cases. The abdominal stigmata are large, the terminal two being very much 
larger than the others 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 
Wing-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 Dytiscidee, although it is com- 
mon in Carabidee ;—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 raised 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 
bezome divisible into two or more aggregates when the various forms become more 
perfected. 
Dytiscus latissimus is most remarkable by the great development 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 (which 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 
