On the Absorption of the Internal Structure of Shells. ' 75 



logue to be good species), only four, viz. Helix euclasta Shuttl, 

 H. incerta Fer., Spiraxisf ejuncida Shuttl, and Achatina subtilis 

 Shuttl, are peculiar to the island, while no less than seventeen 

 of the species are known, on the like testimony, to occur in 

 Portorico, having been collected there by the late Mr. Blauner 

 for Mr. Shuttleworth. On the other hand, at least nine of the 

 species inhabit St. John, — a number very likely to be increased 

 by further researches in that island. It may be remarked that 

 H. euclasta Shuttl. is closely represented in Portorico by H. mu- 

 sicola Shuttl, — H. incerta Fer. by JET. notabilis Shuttl. in St. 

 John, &c, and S. t ejuncida Shuttl. by B. gracillimus Pfr. in Cu- 

 ba, &c, so that the peculiarities of the fauna of St. Thomas, as 

 regards land shells, are trifling. In the larger islands, especially 

 Cuba, Hayti, and Jamaica, the proportion of species found ex- 

 clusively in each is very considerable. The species which have 

 the widest distribution in the West Indies, seem to be those 

 which from their habits are most liable to removal by human 

 agency ; but the opinion now gaining ground, that many indi- 

 viduals of a species were originally created in different parts 

 of its geographical area, must not be overlooked. 



XIII. On the Absorption of Parts of the Internal Structure of 



their Shells, by the Animals of STOASTOMA, LuciDELLA, Tro- 

 CHATELLA, HELICINA, and PROSERPINA. 



By T. Bland. Read February 27, 1854. 



The power which mollusks possess of dissolving portions of 

 their own shells has been long known. This power is exerted 

 by some with a view to remove impediments to their growth, — 



