60 HELIX THELIDOMUS. 



Distinguished from H. aspera by the smooth surface, dark cloud- 

 ed coloration, and (generally) edentulous columella. 



H. DISCOLOR Ferussac. PI. 5, figs. 45-47. 



Imperforate, depressed, opaque, somewhat shining, rather thin, 

 with a thin rich yellowish-brown cuticle, generally encircled just 

 above the periphery with a white band, just below with a dark one ; 

 the whole surface under a lens seen to be marked with slight incre- 

 mental marks, very numerous spiral impressed lines, and obliquely 

 descending microscopic corrugations. There are also on most speci- 

 mens rather coarse, but superficial radiating undulations visible 

 above ; apex nearly planulate ; suture linear, becoming impressed ; 

 whorls 3J to 4, the inner two nearly smooth, scarcely convex, the 

 outer whorl transversely dilated, rapidly widening, subcarinate or 

 rounded at the periphery, tumid beneath, slightly deflexed and quite 

 inflated above toward the aperture; aperture oblong, wide ; peristome 

 re volute, thick, brown ; baso-columellar margin adnate to the base, 

 thickened by a plate-like callus within, its edge more or less ir- 

 regular and sinuous. Alt. 23, diam. maj. 38, min. 30 mill. 



Martinique ; Cayenne ; Trinidad () 



H. discolor Fer., Hist., t. 46, f. 3-6. PFR., in Conchyl. Cab., t. 

 9, f. 11, 12. REEVE, Conch. Icon., f. 253. 



Quite a distinct form. The microscopic sculpture, brown peristome 

 and sinuous, subhorizontal columella are diagnostic characters. 



* * * 



Shell unicolored, straw-color or golden-brown with a few narrow 

 darker longitudinal streaks ; surface striate or decussated ; aperture 

 white within. Species of Cuba and the Bahamas. 



A. Surface decussated by microscopic impressed spiral lines, which 

 cut the incremental striae. 

 H. PETITIANA d'Orbigny. PI. 5, figs. 42-44. 



Imperforate, large, depressed, sub translucent, slightly shining, 

 pale straw-colored, apparently smooth, but under a lens seen to be 

 cut into excessively fine granules by the decussation of incremental 

 stria3 by spiral impressed lines ; spire very small, short, conoidal, 

 obtuse ; sutures impressed ; whorls 4, convex, rapidly increasing, the 

 last about as wide as all the inner ones together, with convex, full, 

 outlines, deeply deflected toward the aperture ; aperture oblong, very 

 oblique ; peristome broadly reflected, adnate to the base ; columellar 

 margin flattened, with a truncated plate-like callus within. 



Alt. 33, diam. maj. 68, min. 50 mill. 



