170 



marine bodies by a short, tendinous pedicle; the beak of the larger valve 

 produced, curved, perforated at the summit, by a round hole, or by a notch; 

 hinge with two teeth; two nearly osseous, slender, elevated, forked, various- 

 ly ramified branches rise from the disk of the small valve, and serve as a sup- 

 port to the animal. 



Lingula. Shell subequivalve, flattened, ovate-oblong, truncated at the 

 summit, rather pointed at the base, elevated on a fleshy, tendinous pedicle, 

 fixed to marine bodies. Hinge without teeth. 



L. anatina. 



mmmi) ©itei$< 



MOLLUSCA. 



Body sometimes naked, either destitute of any solid internal parts, or in- 

 closing a shell or other hard substance, and sometimes provided externally ivith 

 a shell covering or sheathing, but is never composed of two opposite valves 

 united by a hinge. 



This class is divided into five orders, viz. — Pteropoda, Gasteropoda, 

 Trachelipoda, Cephalopoda, and Heteropoda. 



ORDER I. PTEROPODA.— Six Genera. 



Some only are furnished with a thin, cartilaginous or corneous shell. 



HyaLjEA. Shell corneous, transparent, ovate-globose; tridentated poste- 

 riorly; open at the summit, and at the two posterior sides. 

 H. tridentata, H. cuspata. 



