208 SOUTH AMERICAN OPEAS. 



Towards the apex there is some appearance of puckering be- 

 low the suture. The spire tapers straightly and is slender 

 above, as in typical 0. gracile. The smooth apex is conspicu- 

 ously obtuse. The aperture is oblique, long-ovate or pirif orm ; 

 and the columellar margin is rather narrowly reflexed, ap- 

 pressed except for a small crevice. A specimen before me 

 was received from Mr. Guppy about 40 years ago. Three 

 Trinidad specimens measure : 



Length 13.5, diam. 3, aperture 3.2 mm. ; whorls 8%. 



Length 14, diam. 3.1, aperture 3.5 mm;, whorls Sy 2 (fig. 75) . 



Length 12.8, diam. 3, aperture 3.4 mm. ; whorls 8. 



A series before me from Demerara (pi. 29, figs. 76, 77) 

 consists of smaller but evidently adult shells, imperforate or 

 nearly so. 



Length 10.2, diam. 2.5, aperture 2.9 mm. ; whorls 7 (fig. 76) . 



Length 9.5, diam. 2.5, aperture 2.9 mm. ; whorls 6% (fig. 77). 



In other respects they are like the Trinidad shells. Some 

 of them show irregularly scattered whitish spots due to inci- 

 pient disintegration of the surface. Guppy has described a 

 small form also from Trinidad. 



Var. amazonicum n. var. PL 29, fig. 78. 



Shell imperforate, more slender and elongate, but like 

 octogyrum and plicatellum in the yellowish tint and in sculp- 

 ture. Closely peppered with whitish dots. Length 10.2, 

 diam. 2.2, aperture 2.5 mm. ; whorls 8^/2- The type contains 

 two large eggs in the penult, whorl. Para, Brazil (Dr. 

 Hubbard) . 



12. 0. RARUM Miller. PL 29, figs. 82, 83. 



Shell narrowly perforate, oblong-turrite, thin, corneous, 

 brownish above, very glossy; spire convexly conic, the apex 

 rounded. Whorls 7, convex, parted by a deep suture, the last 

 not a third the total length; columella somewhat twisted, 

 receding below. Aperture oblique, suboval, strongly receding 

 below; peristome simple, the right margin slightly arcuate, 

 columellar margin narrowly reflexed adnate above. Length 

 8, diam. 2.6, aperture 2.5 x 1.5 mm. (Mill.). 



