100 



HELIX. 



A. Whorls compressed, or acutely carinate, 

 (Plate XX. fig. I.) (Plate XXVI. fig. 1.) 



B. Umbilicate, whorls rounded, (fig. 2.) 



C. Imperforate, whorls rounded, (fig. 3.) 



D. Tapering, (fig. 4.) 



E. Ovate, imperforate, (fig. 5.) 



Shell univalve, sjjiral, subdiaphanous, brittle. 

 Ai)crture coarctutc, lunate, or circular, having the 

 segment of another circle taken from the whole 

 area; often obovatc. 



The whorls arc contiguous, and there is not the 

 bmallest columellar lip in this genus, but the body 

 uniformly projects convcxly into the circumference 

 of the aperture. In a single species of division A, 

 the one figured in our plate, the whorls are cari- 

 nate longitudinally, instead of transversely, so as 

 to form a flattened two-edged shell. This in 

 Gmelin's edition of the " Systema Naturae" con- 

 stitutes a section bv itself; but as it answers to the 

 terms of the definition of the next division, it is 



