On Aquatic Carnivorous Coleoptera or Dytiscide. 829 
forward as it proceeds to the middle, and on the middle is very nearly obliterated, 
thus the second segment is extremely short in the middle, while the third is nearly 
twice as long in the middle as it is at the side, the three apical segments are short 
and freely flexible on one another. 
The wing-case has a conspicuous epipleura accurately adapted to the mesoster- 
num and metasternum ; at the side of the first ventral segment it becomes much 
narrower, and extends as far as the hind border of the fourth segment, where it has 
very nearly become attenuate to an edge: the extremity of the elytron is sinuate 
and its sutural angle rather acutely rectangular ; the inner face shows two peculiar 
structures ; first, near the outer edge about the middle is a raised process, a short 
irregular elevated plica or fold placed so as to form a cavity, in which the raised 
edge of the first and second ventral segments is received ; second, at the extremity 
near the suture is a raised longitudinal band marked by transverse strize. 
The dorsal sezments of the hind body are provided with small round stigmata, 
the one on the apical segment being quite minute; the ventral segments bear at 
their upper edge a narrow longitudinal band covered by the epipleura, and the 
basal one is provided at its posterior margin, at the junction with the second seg- 
ment, with a raised prominence which fits to the cavity on the inner face of the 
elytron as already described ; and the apical ventral segment is bordered by a sharp 
thin lamina. 
The legs are slender, they are not modified for swimming by any flattening, 
incrassation or dilatation ; on the other hand they are provided with a very elon- 
gate conspicuous ciliation ; the front tibize bear two elongate stout spurs, apparently 
very near to one another, but really inserted on the posterior aspect of the tibia, 
the inner one above, the outer one below the articular cavity ; both the outer and 
the inner edges of the tibia are ciliate, and the outer one besides is armed with fine 
spines. The middle legs are rather elongate, and are not very dissimilar to the 
anterior ones. The hind legs are elongate and slender, each side of the tibia is 
furnished with long ciliz, and the upper and under borders of the slender tarsus are 
likewise greatly ciliate ; the tarsus is twice as long as the tibia, and when the ciliz 
are carefully spread out it can be seen that the lower face of the tarsus is not an 
edge, but a narrow distinct sole ; the two terminal claws are moderately long and 
nearly equal. 
The male anterior and middle tarsi are elongate and slender, but still distinctly 
dilated and incrassate ; the elongate basal joint becomes broader at the extremity, 
and underneath is furnished at the apex with a dense glandular pubescence ; the 
2nd and 8rd joints bear a similar pubescence, the 4th joint is quite visible, but 
small, the 5th elongate, about as long as the basal one. 
The individuals of this genus possess the faculty of stridulating, and the sound 
produced is I believe more powerful than what is made by any other beetle : it is 
5 02 
