ASTACUS. 
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marked with three or four longitudinal, punctated 
furrows ; each finger is armed with a row of obtuse, 
cylindrical spines, which are mutually received and 
inserted, when tlie claws are shut. The claws, 
including the pincers, are ecpial to twice the length 
of the thorax. 
There are five legs on each side ; the anterior 
pair is didactyle ; the others appear to terminate 
in swimmers or paddles, but this circumstance 
cannot be accurately determined. The abdomen 
is composed of six gramdated arcuate segments. 
The tail is foliaceous, marginate, granulated, and 
has a few longitudinal ridges ; but the only known 
sj)ecimen does not exhibit the entire form. 
This species appears to be distinguished from 
the recent animals of the genus, by the dorsal 
ridge and lateral sidci of the thorax ; the gi'eat 
length and straightness of the pincers ; and the 
peculiar form of their spinous processes : a claw 
is figured below : (Jig 1.) 
