238 ASTACID.f:. 



The carapace in tlie present species is granulated, the 

 surface of the sides being scabrous and coarsely granulated. 

 The rostrum is of moderate length, with a tooth on each 

 side, about one-third from the apex : there is a slight ele- 

 vation along the median line, and the margin is also 

 distinctly raised. There is a small tooth on each side 

 of the gastric region, near the base of the rostrum ; and 

 a spine at the anterior part of the branchial. The anterior 

 pair of legs are thick and rounded, covered with tubercles, 

 which become slightly spinous in some parts ; the wrist 

 denticulated on the inner margin ; the hand shorter than 

 the fingers, slightly denticulated on the inner margin ; the 

 fingers curved at the points, and strongly tuberculated 

 on the inner edge. The second and third pairs of feet 

 slender, didactyle ; the fourth and fifth monodactyle. The 

 abdomen is very convex, and rounded above, each seg- 

 ment terminating at the sides in a sharp triangular pro- 

 cess. The terminal segment or central lamina of the 

 tail, evenly rounded at the extremity ; the lateral lamina 

 fan-shaped, the outer one slightly jointed about one-third 

 from the extremity. 



General length, from three to four inches. 

 Colour, a dull greenish gray. 



Few species are more abundantly diffused than this. It 

 is found in almost all the rivers and larger streams, not 

 only of this country, but throughout the greater part 

 of Europe. It is not unfrequently brought to the London 

 market as an article of food, but is not very highly 

 esteemed. It has long possessed a considerable degree of 

 interest, in consequence of the facilities which it affords 

 for watching its habits, and continuously tracing its his- 

 tory ; and it afforded to Reaumur the means of his very 

 interesting and original investigation into the curious 



