918 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



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 

 leno-ths on the hind tarsus ; the smaller spur of the hind tibia is largely bifurcate 

 at the apex ; the epipleurce are not broad, and the females have no sexual sculpture. 



The species of Megadytes are peculiar to South America, where they have a great 

 rancfe, from Mexico to Buenos Ayres, including the Antilles. 



I. 7^.— Geims CYBISTER. (Fu7ep. 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 axillaiy plicte or rugpe, near the articulation of the swimming 

 leg. The species of this group are peculiar to North America. 



B. Nos. 1122 to 1134. — Elytra without a lateral yellow stripe, male with rudi- 

 mentary second claw ; male destitute of axillarj' rugae. The species are found in the 

 tropical regions of the Old World (Asia and Africa). 



C. Nos. 1135 to 1139. — In this group the females are without rudimentary 

 second claw ; in other respect;? they agree with group B, the elytra being without 

 lateral yellow stripe, and the males destitute of axillary rugje. 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 11.51. — Elytra with a yellow lateral stripe which extends to, and 

 includes the epipleurre ; female without any trace of a second claw on hind foot. 



E. Nos. 1152 to 11G8. — 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 1 171. — This group is distinguished by a peculiarity in the females, 



