2M) THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



rather more convex than the posterior, in the females. 

 The tergal surface of the telson is not divided into two 

 parts hy a suture (fig. 61, I). The anterior process of 

 the epistoma is of a broad rhomboidal shape, and there 

 are no distinct lateral spines. 



The squame of the antenna is not so broad relativel}' 

 to its length ; its inner edge is less convex, and its outer 

 edge is slightly concave ; the outer basal angle is sharp 

 but not produced into a spine. The opposed edges of 

 the fixed and movable claws of the chelae of the forceps 

 are almost straight and present no conspicuous tubercles. 

 In the males, the forceps are vastly larger than in the 

 females, and the two claws of the chelae are bowed out, so 

 that a wide interval is left when their apices are applied 

 together ; in the females, the claws are straight and the 

 edges fit together, leaving no interval. Both the upper and 

 the under surfaces of the claws are almost smooth. The 

 median ridge of the endopodite of the sixth abdominal 

 appendage is more marked, and ends close to the margin 

 in a small prominent spine. 



In the females, the posterior division of the sternum of 

 the penultimate thoracic somite is prominent and deeply 

 bilobed ; and there are some small differences in form in 

 the abdominal appendages of the males. JMore especially, 

 the rolled inner process of the endopodite of the second 

 appendage (fig. 62 F, /) is disposed very obliquely, and 

 its open mouth is on a level with the base of the jointed 

 part of the endopodite (g) instead of reaching almost to 



