On Aquatic Carnivorous Coleoptera or Dytiscidce. 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 strise. 



The dorsal segments 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 seo-- 

 ment, with a raised prominence which fits into 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 tibise 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 cilise, 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 ciliae 

 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 3rd 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 O 2 



