y-t'i On Aquatic Carnivorous Coleoptera or Dytiscidce. 



the front tarsi being more elongate, while the palettes are nearly circular in form, 

 and without the papery external prolongations). 



The intermediate tarsi of the male are sometimes furnished beneath with fine 

 sexual jjubescence, but are sometimes quite destitute thereof; the claws are some- 

 times distinctly, but never greatly, elongate, and are never slender. 



The claws of the hind feet differ considerably in the group, the differences being 

 of sexual and specific, as well as of generic importance : they are always however 

 extremely differentiated from the normal, or Cai'aboid, structure. The females, 

 besides sometimes possessing a sexual sculpture, have often a peculiar form of the 

 epipleura, inasmuch as this part near the base is flattened and twisted up so as to 

 assume a more perpendicular direction: this torsion extends to different lengths 

 according to the species, it generally commences a little behind the shoulder, and 

 terminates before the middle or about the middle of the leng'th of the wino^-case. 

 The males have always the underside of the posterior tarsi furnished at both edges 

 with fine swimming hairs, while in the females such cilise are present only on the 

 inner edge, except in the case of one or two species of Cybister, in which the hind 

 tarsi of the females are ciliate on both edsjes as in the males. 



The stigmata of the hind body are all small, and are nearly circular", and difi'er 

 little from one another in size or structure, except in the case of that on the apical 

 segment, which is very small and circular, and passes through the integument in 

 an oblique direction so as to form a sort of tube ; it is in fact formed as if it were 

 made by a needle being pushed through the dorsal plate in the direction of the long 

 axis of the body, instead of at right angles to it. 



The presternum is greatly thickened along the middle so as to give it extreme 

 strength ; the thickening is sometimes so great that, being truncate in front, there 

 is an exposed perpendicular face of considerable length at the front edge in the 

 middle ; the prosternal process is short and thick, and gradually acuminate towards 

 the acute apex, which is received into an impression of the metasternum of just the 

 same form as the termination of the process itself; very little mobility is allowed 

 by this articulation. In some of the Australian forms the presternum shows a 

 deep longitudinal channel along the middle. 



The terminal portion of the wing of the metasternum is always very short (in the 

 direction of the long axis of the body) owing to the fact that the upper border of 

 the hind coxa, when it approaches its antero-external termination, is deflexed 

 abruptly so that its termination is about at right angles to its previous direction; 

 this peculiar and characteristic form of the metasterual wing is however departed 

 from by the Australian genus Spencerhydrus. 



There is usually a distinct, or even considerable, space between the point of the 

 metasternal lacinia and the epipleura ; in some cases however (Uybister latus. No, 

 1,105, and Spencerhydrus pulchellus, No. 1097) this interval is greatly reduced: in 

 some species (Nos. 1,103 and 1,104) the termination of the metathoracic epimeron 



