On Aquatic Carnworous Coleoptera or Dytiscide. Hila 
1. 78.—Genus MEGADYTES. (Vide p. 704.) 
Sixteen species are included in this aggregate; they show much variety in 
several respects, but agree in that the males have the tarsi of the swimming legs 
terminated by two claws, either very nearly equal, or the inner one rather less than 
the other ; the females like the males have always two claws, but the inner one is 
frequently small and rudimentary ; the unguicular cleft is acuminate at its origin. 
The genus thus differs from Cybister, in that there are always two claws on the 
hind tarsi, and that these are more developed in the males than in the females, 
while in Cybister, when there is a difference between the sexes in this respect, it 
is that the females have the claws more developed than the males. 
The species show considerable variety in certain respects and seem to be naturally 
arranged in three groups, viz, A. (Nos. 1103 to 1110, Dytiscus levigatus and 
allies) claws of hind feet in male two in number, of equal or nearly equal lengths, in 
the female a single long claw with a much more rudimentary one on its under and 
inner side ; the smaller spur of the hind tibia simply acuminate at the extremity. 
This group is heterogeneous and contains at any rate four, if not more, distinct 
forms, viz.: 1, (M. expositus and Cybister glaucus) species of moderate size with 
vague yellow lateral band on the wing-case, and with the termination of the 
lacinize of metasternum far from the epipleura, and the termination of the meta- 
thoracic epimeron very distinctly exposed ; the two species are widely discrepant 
in certain other respects. 2, (Dytiscus latus) a species of smaller size, without 
yellow band on the wing-case ; the lacinia of the metasternum closely approximate 
to the epipleura, and no portion of the metathoracic epimeron is exposed; the 
character that separates this species widely from the third sub-group is that in the 
male the inner claw of the hind foot is decidedly shorter than (as well as finer than) 
the outer one. The female has a sexual sculpture of excessively short punctiform 
lines. 3, (Nos. 1106 to 1109, Dytiscus leevigatus, &c.,) like the preceding, of rather 
small size (at most 24 m.m. long), with or without yellow band on elytron, and 
the inner claw on the hind tarsus of the male quite as long as the other ; the females 
have a very beautiful sexual sculpture consisting of deep, regular, short, almost 
punctiform lines. 4, (Cybister puncticollis), this species is imperfectly known ; it is 
of rather large size (about 30 m.m. long), the elytra have a yellow stripe, the 
lacinize of the metasternum are approximate to the epipleure, and the apex of the 
metathoracic epimeron is not exposed ; the female is without sexual sculpture ; this 
species in appearance resembles those of group B ; its male is unknown. 
The second group, (B) is more homogeneous, although the width of the epipleuree 
varies much in the different species; in it each sex has on the hind tarsus two 
claws of nearly equal lengths; the smaller spur of the hind tibia is minutely 
tridentate or trituberculate at the apex ; the species are six in number (Nos. 1111 
to 1116), and are of moderate or large size, the epipleuree of the elytra are frequently 
6 B2 
