Astacilla longkornis. 



495 



«, Astactlla longic6rnis, of the natural size ; 5, the three outer joints of the superior antenna, 

 greatly magnified ; c, the same of the inferior antenna ; d, a leg of the first pair ; e, one of 

 the swimming legs j /, one of the creeping legs j g, one of the branchial abdominal pro- 

 cesses. 



as long as the body, crustaceous, roughish, tapered, with 

 seven joints, of which the first is very short, the second twice 

 as long, the third and fourth still longer and nearly equal, the 

 three terminal slender, short, sparingly hispid and serrulated 

 underneath with a close series of spinous denticles : post- 

 occipital segment united immovably to the head, transverse 

 with dilated sides, its pair of legs short, directed forwards 

 over the maxilla?, six-jointed, the thigh moderately elongate, 

 the next joint forming a sort of knee, the third also short, the 

 fourth and fifth longer and dilated, the terminal small and 

 compressed, and all, except the thigh, densely ciliated along 

 the inferior surface, the ciliae in two marginal rows and 

 plumose : two next segments of the body short, transverse, 

 arched, tuberculate, with a dilated process on each side that 

 overhangs the tubercles from which the swimming feet arise ; 

 the fourth segment is very large, equal in length to one half 

 of the body, rounded and granulous on the back, and with a 

 granular ridge on each side, separated by a smooth line, the 

 ventral surface smooth and membranous, the front margin 

 dilated laterally like the two preceding segments, and bearing 



M M 4 



