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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. 



T. vitrea, 



T. flavescens, 



T. caput serpentis, 



T. rosea, 



' dilatata, 



' dentata, 



' truncata, 



' rubra, 



* pisum, 



' dorsata, 



' psittacea, 



' bivulnerata, 



' globosa, 



' sanguinea, 



' pulchra, 



47 fossil species, 



' rotunda, 









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. 



MOLLUSCA. 



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

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

 a shell covering or sheathing, but is never composed of tivo 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. 



Hyal^ea. Shell corneous, transparent, ovate-globose; tridentated poste- 

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



II. tridentata, II. cuspata. 



