HELIX-DENTELLARIA. 85 



within two denticles, or irregularly denticulate; upper and lower 

 margins subparallel, terminations remote, joined by a heavy brown 

 callus, which under a lens is seen to be very minutely granulate. 

 The upper margin is very much thickened upon its face, often 

 obtusely lobed. Alt. 14, diam. 23 mill. ; alt. 10, diam. 18 mill. 



Guadeloupe ; Martinique ; Cayenne. 



H. dentiens FER. Prodr. 88 ; Hist. t. 48, f. 2 ; t. 49 A, f. 2. WOOD. 

 Ind. Test. Suppl. t. 7, f. 48. PFR. in Conchy 1. Cab. p. 110, t. 15, f. 

 11-13 ; Monogr. i. p. 107. GUPPY, Ann. and Mag. N. H. 4th ser. 

 i, p. 431. Dentellaria dentiens W. G. BINNEY, Ann. N. Y. Acad. 

 Sci. iii, p. 111. 



There is a mutation which may be called var. isabellina, char- 

 acterized by a pale greenish-yellow or an isabella color all over, the 

 peristome and parietal wall white. Sometimes bifasciate with brown. 

 It is from Guadeloupe. 



This shell differs from H. obesa in lacking a tooth on the parietal 

 wall at its junction with the upper termination of the peristome; 

 from H. isabella by the gibbous ridge behind the peristome, and the 

 granulate parietal callus and peristome. This last character is 

 microscopic, but it holds good through the large suites of each 

 species before me. I consider the two species perfectly distinct. 



H. ISABELLA Ferussac. PI. 24, figs. 42, 43. 



Imperforate, depressed, solid, opaque, shining, obliquely striatulate, 

 rarely showing faint traces of spiral impressed lines under a strong 

 lens, whitish or greenish yellow, with two brown bands, which are 

 generally wide, fading into the ground-color on their outer edges, 

 leaving between them a narrow, well-defined peripheral light fascia ; 

 center of the base light colored. Spire low, rounded, obtuse ; apical 

 whorl flat ; sutures linear, becoming impressed around the outer 

 whorl ; whorls 4s, slightly convex, slowly widening, the last subangu- 

 lar or rounded at the periphery, a trifle contracted behind the aper- 

 ture, scarcely descending anteriorly. Aperture very oblique, oblong- 

 lunar, transverse ; peristome heavy, thick, brown or brown and 

 white, upper and basal margins parallel, the latter thickened within, 

 the edge of the thickening more or less irregular or subdenticulate, 

 whitish, right margin slightly expanded, terminations of peristome 

 joined by a smooth shining parietal callus. 



Alt. 13, diam. 23 mill. ; alt 11, diam. 20 mill. 



Barbados ; Guadeloupe ; Cayenne. 



