254 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



extended to touch the adjoining whorl. Above the posterior angle 

 of the aperture the peristome forms a triangular projection merging 

 into a siphon which recurves and points back toward the adjacent 

 whorl, though not usually forming a contact with it. The siphon 

 communicates with the interior of the shell by a hole just within the 

 aperture. The operculum is typical. 



Type. — A female specimen, Cat. No. 314951, U.S.N.M., was col- 

 lected by Torre at Paso de Lesca in the Cubitas Mountains, 

 Camaguey Province, Cuba, and measures: Length, 12.8 mm.; greater 

 diameter, 9.75 mm.; lesser diameter, 7.4 mm.; length of aperture 

 within, 5 mm.; width of aperture within, 4 mm. A male specimen 

 from the same locality measures: Length, 10.9 mm.; greater diame- 

 ter, 9 mm.; lesser diameter, 6.4 mm.; length of aperture within, 

 4 mm.; width of aperture within, 3.5 mm. 



This species is characterized by its open umbilicus, moderate 

 expansion of the peristome, inconspicuous sutural crenulation, and 

 its shining surface. 



OPISTHOSIPHON (OPISTHOSIPHONA) DALLI Torre and Henderson. 



Plate 40, figa. 2, 8, 9. 



Opisthosiphon dalli Torre and Henderson, A New Opisthosiphon from Cuba. 



Privately published June 25, 1920. 

 Opisthosiphon (Opisthosiphona) dalli Henderson and Bartsch, Proc. U. S. Nat. 



Mus., vol. 58, p. 68, 1920. 



The shell is turbinate, solid, widely umbilicated, with the apex 

 decollated, leaving three and a half to four convex whorls, the last 

 being solute for a short distance, and carinated at the summit of the 

 solute portion. The shell is of a pale brown color without trace of 

 either bands or spots, the apical portion being conspicuously light 

 reddish. The sculpture consists of densely crowded axial threads 

 which are somewhat more distantly spaced upon the earlier post- 

 nuclear whorls. Some of these axial threads are veiy minutely 

 expanded into denticles at the summit, but not sufficiently so to lend 

 a crenulated appearance to the deeply impressed sutures. The spiral 

 sculpture consists of about ten or twelve low rounded cords within 

 the umbilicus. The vertical aperture is roundly oval with a posterior 

 angle. The peristome is not obviously double as the inner peritreme 

 is but slightly expanded and reflected over and appressed to the outer. 

 The outer peritreme is but slightly expanded on the outer side; on 

 the inner side it is flatly expanded, though not sufficiently so to cover 

 any portion of the umbilicus, nor more than sufficient barely to touch 

 the preceding whorl. At the posterior angle of the aperture the 

 peristome extends into an upward expansion forming an open siphonal 

 tube. The operculum is typical of the genus. 



Type.— Cat. No. 314941, U.S.N.M., is from the cave of El Circulo. 



