240 THE COMPAllATIVE MORPHOLOGY OF THE CRAYFISH. 



The apex of the dactylopodite, like that of the propo- 

 dite, is formed hy a slightly incurved spine (fig. 20), while 

 its outer, sharper, edge presents a curvature, the inverse 

 of that of the edge of the fixed claw against which it is 

 applied. This edge is beset with rounded tubercles, the 

 most prominent of which are one at the beginning, and 

 one at the end of the concave posterior moiety of the edge. 

 When the dactylopodite is brought up to the fixed claw, 

 these tubercles lie, one in front of and one behind the 

 chief tubercle of the convexity of the latter. The whole 

 surface of the prox3odite and dact3doj)odite is covered 

 with minute elevations, those of the upper surface being 

 much more prominent than those of the lower surface. 



The length of the fully extended forceps generally 

 equals the distance between the posterior margin of the 

 orbit and the base of the telson, in well characterized 

 males ; and, in individual examples, they are even longer ; 

 while it may not be greater than the distance between 

 the orbit and the hinder edge of the fourth abdominal 

 somite, in females ; and, in massiveness and strength, the 

 difference of the forceps in the two sexes is still more 

 remarkable (fig. 2). Moreover there is a good deal of 

 variation in the form and size of the chelae in mdividual 

 males. The right and left chelae present no important 

 differences. 



The ischiopodites of the four succeeding thoracic limbs 

 are devoid of any recurved spines in either sex (Front., 

 fig. 40). The first pair are the stoutest, the second the ' 



