ANOSTOMA 



Fischer Tabulae iZoognosiae. 

 Lam. — Anim. sans vert* vi. p. 2, 100. 



TESTA orbicularis, sublenticularis, spira convexa, 

 obtusa. Apertura semilunaris,, sursum, supra 

 spiram, reyersa, utrinque dentata. Labium exter- 

 num incrassatum, reflexum, internum supra spi- 

 ram expansum. 



The peculiarity which distinguishes this Genus from all 

 the other heliciform univalves is so extraordinary, that it 

 appears to us to be deserving of particular notice, inas- 

 much as it evidences a considerable alteration in the habit 

 and economy of the animal which produces it, at the time 

 of its arrival at its last period of growth, when it forms 

 the reflected outer lip and the teeth in the aperture ; until 

 then the animal must crawl about, like other snails, with 

 the spire of its shell uppermost ; but as soon as it arrives 

 at maturity and is about to form its complete aperture, it 

 takes a reverse position, and afterwards constantly carries 

 its spire downwards. Our ignorance of the peculiar mode 

 of life and habitation of this animal may tend to make this 

 fact appear the more singular, whereas if we had the op- 

 portunity of ascertaining these, we should, perhaps, find 

 that it is only a wise provision of nature for the safety of 

 the animal or the perpetuity of the kind. In other re- 

 spects, the shell bears a strong resemblance to the Helices^ 

 for which reason Linne has classed it with them ; doubt- 

 less, the animal also nearly resembles that of Helix^ though 

 we cannot here speak with certainty, because we have 

 never seen it, nor do we believe, that there is either de- 

 scription or figure of it extant. 



In its general form the shell is orbicular, sublenticular, 

 the spire being convex, but obtuse and forming one side of 



