22 PALUDINID^. 



Turbo ciistatus, Maton and Rack. Trans. Linn. Soc. vol. viii. p. ll)9. — TliRT. 

 Contli. Diction, p. 227. — Dillw. Recent Shells, vol. ii. 

 p. 883.— Wood, Index Testae, pi. 32, f. 163. 



A certain degree of variation is produced in this long- 

 known species, from the looseness of its coil, which causes 

 the spire to appear at one time nearly level, at another time 

 somewhat sunken. The peristome at times, too, bends 

 slightly backwards, at other times it is simple. Hence, we 

 believe, has arisen the distinction between the V. spirorlis 

 and V. planorhis, as it appears in certain writers ; yet 

 Draparnaud's figure of the latter exhibits a more slowly- 

 enlarging shell than any of our adult British speci- 

 mens. 



The shell is discoid, thin, semitransparent, glossy, and 

 of a rather pale horn-colour, smooth to the eye, but under 

 the lens densely and distinctly, though partially, wrinkled 

 in a longitudinal direction. The upper disk is flattish, the 

 spire being rather sunken than otherwise ; the middle of the 

 lower disk is broadly and deeply excavated, and thus exposes 

 all the preceding volutions. The three cylindrical whorls 

 are a little flattened both above and below ; they enlarge, 

 with moderation, from a not very small apex, and are dis- 

 tinctly separated by a suture, that, from the abruptness 

 of their elevation, appears the more profound. As the volu- 

 tions are not very tightly coiled, nearly their entire extent 

 is visible in the vast umbilical cavity ; the flatness we liave 

 also referred to, is not apparent underneath towards the 

 mouth : the circumference is well rounded. As the last 

 turn does not clasp the preceding one, the aperture is 

 circular, yet the curve, for the most part, is a little flattened 

 upon the pillar. It occupies fully one-third of the basal 

 diameter, is simple, acute, yet more or less expanding 

 when adult, and manifestly projects below the basal level. 



