100 



HELIX. 



A. Whorls compressed, or acutely carinate, 



(Plate XX. Fig. 1.) (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, spiral, subdiaphanous, brittle. 

 Aperture coarctate, lunate, or circular, having the 

 segment of another circle taken from the whole 

 area ; often obovate. 



The whorls are contiguous, and there is not the 

 smallest columellar lip in this genus, but the body 

 uniformly projects convexly 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 by itself ; but as it answers to the 

 terms of the definition of the next division, it is 



