918 On Aquatic Carnivorous Coleoptera or Dytiscide. 
very broad ; the females differ greatly as regards sexual sculpture, which is some- 
times very highly developed, sometimes quite absent. 
The third group, (C,) comprises two species (Cybister giganteus and Megadytes 
ducalis) they are of very large size, and have in each sex two claws of about equal 
lengths on the hind tarsus ; the smaller spur of the hind tibia is largely bifurcate 
at the apex ; the epipleuree are not broad, and the females have no sexual sculpture. 
The species of Megadytes are peculiar to South America, where they have a great 
range, from Mexico to Buenos Ayres, including the Antilles. 
I. 79.—Genus CY BLISTER. (Vide p. 714.) 
This large aggregate comprises fifty species; they differ from the other Cybistrini 
in that the males have only a single claw on the hind tarsus; the females have also 
usually only a single claw, but they possess in certain cases a rudimentary second 
claw placed on the underside and at the inner edge of the larger one ; the unguicular 
cleft is acuminate at the base ; and the prosternum is not channelled. 
The numerous species may be arranged in six groups. 
A. Nos. 1119, to 1121.—Elytra with a yellow stripe, female with rudimentary 
second claw ; male with axillary plice or rugz, near the articulation of the swimming 
leg. The species of this group are peculiar to North America. 
B. Nos. 1122 to 11384.—Elytra without a lateral yellow stripe, male with rudi- 
mentary second claw ; male destitute of axillary rugee. The species are found in the 
tropical regions of the Old World (Asia and Africa). 
C. Nos. 1185 to 1139.—In this group the females are without rudimentary 
second claw ; in other respects they agree with group B, the elytra being without 
lateral yellow stripe, and the males destitute of axillary rugz. It is to be noted 
that individual female specimens of certain species of this group are occasionally 
met with in which there may be detected a very slight rudiment of the second 
claw ; the group therefore cannot be considered as sharply separated from the 
preceding one. 
D. Nos. 1140 to 1151.—Elytra with a yellow lateral stripe which extends to, and 
includes the epipleure ; female without any trace of a second claw on hind foot. 
E. Nos. 1152 to 1168.—Elytra with a yellow lateral stripe which does not quite 
extend to or include the epipleura; female without rudiment of second claw on 
hind foot. In this group C. wehnckianus repeats the peculiarities of C. pectoralis 
of the preceding group, except as regards the yellow stripe on the wing-case. C. 
cephalotes appears at first sight to have the yellow band extending to the epipleura, 
but on a more careful examination it is seen that the raised marginal line is of 
dark colour throughout its whole length so that the species is better placed in 
this group. 
F. Nos. 1169 to 1171.—This group is distinguished by a peculiarity in the females, 
