98 GASTEROPODA. 



tending the whole length of the body ; columella visible to the 

 end. 



Akera flexilis — The Flexible Akera. Plate XIV. fig. 29. 

 Oval membranaceous, excessively thin and flexible; horn- 

 coloured, with a convolute truncated channelled spire ; pillar 

 lip a little thickened and white. Three-fourths of an inch long. 

 Inhabits the British seas. 



Genus 12— DIAPHANA.— ZJroMJTi. 



Generic Character. — Animal unknown. — Shell small, spiral, 

 fragile, somewhat orbicular ; aperture encompassing the body, 

 wide ; pillar lip slightly reflected, behind which is a subumbili- 

 cus ; spire very short, never exceeding two volutions, and hardly 

 rising above the body, which is concave at top. 



Diaphana Candida.— Tre White Diaphana. Plate XIV. 

 fig. 30. Pure white, ventricose ; aperture whole length of the 

 shell, narrowed at top ; spire short ; subumbilicated. One- 

 sixth of an inch long. Inhabits the Frith of Forth. 



Genus 13. — A CERA. — Lamarck. 



Generic Character — Body ovate, convex, transversely divided 

 above into two parts ; the foot with dilations in the form of 

 wings below ; head indistinct ; branchiae situated on the back, 

 greatly behind, and covered by a mantle ; destitute of a shell. 



Acera carnosa. — The Fleshy Acera. Cuvier in Annals 

 du Museum, Plate X. fig. 15, 16. 



TRIBE IV. CALYPTRACEA. 



The branchiae are situated in a dorsal cavity near the neck, 

 and included in the cavity or projecting beyond it j shell invari- 

 ably exterior. 



Ge?ius U.—A'^ CYLUS.— Draparnaud. 



Generic Character. — Body creeping, enveloped in the shell; 

 two compressed subtruncated tentacuia, with the eyes situated 

 at their internal base ; foot short, elliptical ; somewhat narrower 



