HELIX PLAGIOPTYCHA. 21 



This form is allied to duclosiana in the deep-seated, strong tubercle 

 of the base; but differs in being generally smaller, less shining, and 

 in the dark supra-peripheral fascia. 



Imperforate ; columellar lip adnate to the base. 



H. MONODONTA Lea. PL 11, figs. 16, 25. 



Imperforate, globose-depressed, thin but strong, generally opaque, 

 whitish, with usually a supra-peripheral brown fascia, and numerous 

 narrow brown lines, and sometimes sparsely dotted with b lackish or 

 brown ; often nearly unicolored brownish, or subtranslucent cor- 

 neous ; surface scarcely marked by growth-lines, shining, smooth ; 

 spire low-conical, apex subobtuse ; sutures well-impressed ; whorls 

 4 to 4i-, somewhat convex, rapidly widening, the last rounded, very 

 deeply and abruptly deflexed anteriorly; aperture subhorizontal, 

 rather small, oval-truncate ; terminations of the peristome converg- 

 ing; superior lip strongly arched, outer lip arcuate, narrowly expand- 

 ed, baso-columellar margin straight, expanded, adnate toward the 

 center of the base, bearing a strong tubercular fold or tooth on its 

 inner edge. Alt. 8, diam. 13 mill. 



Hayti. 



H. monodonta LEA, Obs. gen. Unio, etc., i, p. 165, t. 19, f. 62, 

 (1831) PFR. in Conchyl. Cab. t. 63, f. 1-4. REEVE, Conch. Icon. 

 f. 294. H. haitensis W. ET M. Malak. EL 1859, p. 17. PFR., 

 Monogr. v, p. 304. H. acuminata, PFR. Zeitsch.f. MaL 1851, p. 16 ; 

 Conchyl, Cab. t. 140, f. 7, 8, p. 373 ; Monogr. iii, p. 190. REEVE, 

 Conch. Icon. f. 785. 



An abundant species, very variable in coloration. The aperture is 

 a little rounder than in H. haitensis, the lip is more expanded, more 

 strongly toothed within, and the shell is usually more variegated. 



Var. HAITENSIS Weinland et Martens. 



The general form and appearance of this shell is like H. mono- 

 donta. It is more fragile, translucent, "isabella-colored," with a 

 sutural opaque white fascia, and often a narrow brown band above 

 the periphery. The peristome is thin, expanded ; the columellar 

 is tooth scarcely developed. Alt. 7-1, diam. 13 mill. 



H. acuminata Pfr. (pi. 11, fig. 26) seems to be the same as H. 

 haitensis in all respects. 



