SHELLS. 213 



Tte single genus Cancer (according to Cuvier) 

 comprising the numerous species of crabs, is divided 

 into sections. Of these, the majority have the legs 

 attached at the sides of the breast, and always 

 exposed. The species thus characterized constitute 

 the first five sections — Pinnipedes, Arcuata, Quadri- 

 latera, Orhiculata, and Trigona. 



Amongst the first section (Pinnipedes), vr& may 

 especially mention a species of swimming crab {Lupa 

 forceps). It is very active and fierce, extending its 

 open claws in a threatening manner when danger is 

 near ; but if allowed to escape by swimming, it does 

 so rapidly, bending up the claw of the side which 

 happens to be foremost, and allowing the other to 

 stretch out behind. Probably this is the arrangement 

 in which these tmwieldy members offer least resist- 

 ance to the water in progression. 



In the second section (Arcuata), we find the com- 

 mon edible crab (Cancer pagurus) of Bermuda. 

 During the summer months it is very abundant in 

 our bays. The carapax is granulated, and arched 

 along the sides, with nine folds on each side, and the 

 middle in front, with three short teeth. 



The third section (Quadrilaterd) have the carapax 

 almost square, sometimes heart-shaped, widened and 

 rounded at the anterior angles, and truncated trans- 



14—2 



