212 PROCEEDINGS OF THE NATIONAL MUSEUM Vol. 89 



broadly expanded on the parietal wall, where it is reflected over and 

 appressed to the preceding turn, and on the inner lip this outer peri- 

 stome is reflected over the umbilicus, almost completely hiding it when 

 viewed squarely; on the basal and outer lip it becomes narrower but 

 it is again expanded into a broad amicle at the posterior angle, where 

 it is rendered irregular by the siphon immediately behind it; inner 

 peristome slightly exserted and slightly expanded. Operculum 

 typically opisthosiphonid. 



The type, U.S.N. M. No. 314953, was collected at La Providencia, 

 El Cercado, Sierra de Cubitas, Camagiiey Province. It has a little 

 over 3 whorls and measures: Length, 11.0 mm.; greater diameter, 7.2 

 mm.; lesser diameter, 5.8 mm. 



Bartsch also collected this species in Paso de Lesca and at Sitio 

 Afuera, at the south end of Paso de la Escalera, Cubitas Mountains, 

 Camagiiey Province. 



Figure 2 shows an extreme variant of the species with an enormously 

 developed outer peristome of the inner lip. This is U.S.N.M. No. 

 355501 and it comes from Paso de los Paredones, and measures: 

 Length, 10.5 mm.; greater diameter, 7.9 mm. ; lesser diameter, G.2 mm 



OPISTHOSIPHON (CUBITASIPHONA) APERTUM Torre and Henderson 



Plate 17. Figure 1 



1920. Opisthosiphon {Opisthosiphona) apertus (Torre and Henderson) Hender- 



son and Bartsch, Proc. U. S. Nat. Mus., vol. 58, p. 67, nomen nudum. 



1921. Opisthosiphon {Opisthosiphona) apertum Torre and Henderson, Proc. 



U. S. Nat. Mus., vol. 59, p. 253, pi. 40, figs. 1, 3. 



Shell ovate, thin, flesh colored, horn colored, pale orange, or pale 

 brown, sometimes unicolor, but usually with a broad brown band at 

 the periphery; peristome white; the interior of the aperture varying 

 with the external color. Nuclear whorls 2, small, well rounded, 

 microscopically granulose, with the last portion of the last turn show- 

 ing the beginning of the postnuclear sculpture. Postnuclear whorls 

 inflated, strongly rounded, marked by very poorly developed, slightly 

 retractively slanting axial riblets, which are more distantly spaced 

 on the early turns than the later. In the type 42 of these riblets occur 

 upon the first turn, 64 upon the second, 140 upon the third, and 160 

 upon the last whorl. Some of these riblets extend slightly above the 

 rest at the summit and fuse to form very weak, almost obsolete cusps. 

 Suture strongly constricted. Periphery well rounded. Base short, 

 inflated, strongly rpunded, marked by the continuation of the axial 

 riblets, and within the umbilicus by 10 spiral threads. Last whorl 

 solute for almost half a turn. Aperture broadly oval; peristome 

 double, the inner slightly exserted and moderately reflected ; the outer, 

 conspicuously expanded on the inner lip and very slightly so on the 

 outer, forming a conspicuous auricle at the posterior angle of the 



