On Aquatic Carnivorous Coleoptera or Dijtiscidce. 917 



\.7^.—Gexm.?iMEGADYlES. (FiV/e p. 704.) 



Sixteen species are included in tliis 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 Isevigatus 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 

 lacinias of metasternum far from the epipleura, and the termination of the meta- 

 thoracic epimevon 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 ajiproximate 

 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 laevigatus, &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 

 laciniee of the metasternum are approximate to the epipleura?, 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 epipleurae 

 varies much in the difterent 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 1 1 1 6), and are of moderate or large size, the epipleuraj of the elytra are frequently 



G B 2 



