100 
HELIX. 
A. Whorls compressed, or acutely carinate, 
(Plate XX, Fig. 1.) (Plate XXVI. Fig. L) 
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 
