74 CLASS III. GASTEROPODA. ORDER VI. PULMOBRANCHIATA. 
when arriving at maturity? Until then, it must crawl about like other 
snails with the spire of the shell uppermost ; but during the formation of 
the last whorl it must suddenly take a reversed position, as in the full- 
grown shell the aperture appears to be on the obverse side to that in the 
Helices, namely, on a plane with the spire, which must then be under- 
most.” 
The shell of Anostoma is described as being orbicular, shaped some- 
what like a lens, and its peculiarity is in having the last whorl suddenly 
turned upwards ; the aperture is semilunar or crescent-shaped, because 
of the penultimate whorl projecting into its cavity, and both sides are 
dentated ; the outer lip is thickened and reflected, and the inner lip is 
spread over the spire. 
Examples. 
Pl. CLXIX. Fig. 1. 
ANOSTOMA RINGENS, Sowerby, Genera of Shells, No.8. Chemn. Conch., 
vol. ix. pl. 109. f. 919, 920. 
Helix ringens, Linneus. 
Anostoma depressa, Lamarck. 
2 De Montford. De Blainville. 
Tomogerus 
Pl. CLXIX. Fig. 2. 
ANOSsTOMA GLOBULOsUM, Lamarck, Anim. sans vert., new edit., vol. vill. 
p. 133: 
Helix (Helicodonta) ringicula, De Férussac. 
PUPA, Draparnaud. 
Testa oblongo-cylindracea, sepé crassiuscula, anfractibus plurimis, ple- . 
rumque transversim costellatis, umbilicum profundum interdum for- 
mantibus ; apertura aut subquadrato-ovali, aut rotundata, intus ple- 
rumque dentata ; margine subcrasso, labro reflexo. 
