240 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 
The apex of the dactylopodite, like that of the propo- 
dite, is formed by 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 propodite and dactylopodite 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 chele in individual 
males. The right and left chele present no important 
differences. 
The ischiopodites of the four succeeding thoracic limbs 
are devoid of any recurved spines in either sex (Front., 
fig. 46). The first pair are the stoutest, the second the 
