248 MOLLUSCA. 



on particular pedicles, and a mouth resembling a more or less elongated 

 proboscis. 



Their tongue is armed with little hooks, and by slow and repeated rubbing 

 acts upon the hardest bodies. 



The greatest difference in these animals consists in the presence or absence 

 of the little canal formed by a prolongation of the edge of the pulmonary 

 cavity of the left side, and which passes through a similar canal or emargina- 

 tion in the shell, to enable the animal to breathe without leaving its shelter. 

 There is also this distinction between the genera some of them have no 

 operculum ; the species differ from each other by the filaments, fringes, and 

 other ornaments of the head, foot, or mantle. 



These Mollusca are arranged in several families according to the form of 

 their shell, which appears to bear a constant relation to that of the animal. 



FAMILY I. 



TROCHOIDA. 



THIS family is known by the shell, the aperture of which is entire, without 

 an emargination or canal for a siphon of the mantle, as the animal has none, 

 and is furnished with an operculum or some organ in place of it. 



TROCHUS, Linnaeus, 



The external margin of the angular aperture approaching' more or less to 

 a perfect quadrangular figure, and in an oblique plane, with respect to the axis 

 of the shell, because the part of the margin next to the spine projects more 

 than the rest. Most of these animals have three filaments on each edge of the 

 mantle, or at least some appendages to the sides of the feet. The 



SOLARIUM, Lamarck. 



Is distinguished from all other Trochi by a very broad conical spire, at the 

 base of which is an extremely wide umbilicus, in which may be seen the 

 internal edges of all the whorls, marked by a crenated cord. 



EUOMPHALUS, Soicerby. 



Fossil shells resembling a Solarium, but wanting the dentations on the 

 internal whorls of the umbilicus. The genus 



TURBO, Linncens, 



Comprehends all the species with a completely and regularly turbinated shell, 

 and a perfectly round aperture. Close observation has caused them to be 

 greatly subdivided. 



These subdivisions are Delphinula, P/eurotoma, Turritella, Scalaria, anil 

 Cycbatomu. The last is terrestrial, and found under moss and stones in woods. 

 The Valvala, another subgenus, is found in stagnant water. 



