﻿45° SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. tf 



translucent interspaces, crossed by much finer, regular, sharply de- 

 fined axial threadlets, most evident in the interspaces and giving a 

 textile effect to the surface ; the revolving threads a little stronger on 

 the base ; umbilicus small, perforate, not covered by the narrow peri- 

 stome ; termination of the last whorl not free from the body ; aper- 

 ture, short, ovate, yellowish, showing the brown spirals internally ; 

 peristome narrow, slightly reflected, little thickened, but somewhat 

 angular behind ; operculum thin, the calcareous layer thin, its dis- 

 position similar to that of Ctetwpoma riigulosum Pfr., the type of 

 the genus RJiytidopoma Sykes. Height of shell 8.0 ; maximum 

 diameter of shell 4.0 ; of aperture 2.6 mm. 



Opisthosiphon baluuiiciisis Shuttleworth. 



Typical locality Nassau ; collected by Mr. Bryant in various locali- 

 ties at and near Nassau ; Great Abaco, on the Sugar Loaves rocks ; 

 Little Abaco near Nield's and Marsh Harbor, and Mathews Point 

 on the south side of Abaco. 



This is the most abundant species of the family in the Bahamas, 

 and, considering its wide distribution, is very uniform in character ; 

 differing chiefly in color, the Nassau variety being frequently of a 

 livid purpuraceous tint while the specimens from the outer and 

 eastern islands are more disposed to assume a yellowish color with 

 fairly distinct dottings or streaks of brown. The differences of 

 size, probably correlated with the food supply, are not very marked. 

 This, with the allied 0. razvsoni Pfr., belongs to a new genus 1 charac- 

 terized by a little tube which is formed behind the posterior angle of 

 the peristome and turned with its aperture close to the surface of 

 the preceding whorl ; so that, when the animal protects itself by 

 hermetically closing the aperture of the shell with the operculum, 

 air can still be admitted through this little tube to the interior, though 

 the orifice is not large enough to give access to any enemy of the 

 species. This tube at a later stage is closed up permanently. 



Specimens of this species in the National Museum were named by 

 Bland C. biformc Pfeiffer, but I am informed by Mr. E. A. Smith of 

 the British Museum that the true biformc is a species of Chon- 

 dropoma. 



Helicina fasciata Lamarck. 



Mangrove Cay, Andros, in dead sisal ; Riding Point, Grand Ba- 

 hama ; Cuba. 



This species appears to be rather rare, as Mr. Bryant obtained only 

 a few immature and one dead adult specimen. It had not previously 



1 Cf. Proc. Malac. Soc. London, vi, p. 209, 1905. 



