HISPANIOLAN AND BAHAMAN ANNULARIIDAE 139 



channeled. Periphery inflated, well rounded. Base strongly rounded, 

 openly umbiUcated, and marked by the continuation of the axial ribs and 

 six spiral cords. The axial ribs extend somewhat weakened upon the um- 

 bilical wall which also bears seven spiral cords. Aperture circular; 

 peristome double, the inner quite strongly exserted ; the outer expanded, 

 forming an auricle at the posterior angle, and a little wider on the outer 

 than on the inner lip, narrowest on the parietal wall. Operculum too large 

 to be withdrawn into the shell. It caps the aperture. It has a central 

 nucleus, and bears a strongly convex thin lamella whose outer edge 

 touches that of the succeeding turn. The lamella is marked by fine, re- 

 tractively curved hairlines. 



The type (U.S.N.M. No. 5040S5) was collected in the crevices of 

 rocks in a ravine a little west of Bombardopolis, Haiti, by Mr. and Mrs. 

 E. C. Leonard. It has 4.9 whorls and measures: Height, 6.5 mm.; 

 greater diameter, 7.1 mm.; lesser diameter, 6.2 mm. 



U.S.N.M. No. 504086 contains 171 topotypes from the same source. 



Genus COLOBOSTYLUS Crosse and Fischer 



1888. Colobostylus Crosse and Fischer, Journ. Conchyl., vol. 36, p. 229. 



Shell ovate, axial ribs present, spiral sculpture absent. Operculum 

 with a strongly calcified lamella, which is reflected to parallel the basal 

 chondroid plate. The lamella of the succeeding turns is in contact with 

 that of the preceding whorls, thus completely covering the outside of 

 the operculum excepting the outer edge of the chondroid plate on the 

 last whorl where this projects materially beyond the edge of the lamella. 

 The lamella is marked by retractively slanting axial threads. 



Type species: Colobostylus jayanus (C. B. Adams), selected by Dall, 

 1905, Proc. Malac. Soc. London, vol. 6, p. 209, 1905. 



Typical Colobostylus is not known from Hispaniola. Here it is re- 

 placed by the subgenus Colobostyloides. 



CoLOBOSTYLOiDES, new subgenus 



Shell small, ovate, openly umbilicated, ornamented with axial ribs 

 only. Aperture with double peristome. The operculum is too large to be 

 withdrawn within the aperture, but caps this. It consists of a basal 

 chondroid plate and a strongly calcified lamella, which is reflected to 

 parallel the basal plate. The adjacent turns of the lamella touch, thus 

 forming a continuous outer surface; they are marked by retractively 

 curved raised threads. 



Type species: Cydostoma saxormn Weinland = Co/o&o.yfy/Mj' (Colo- 

 bostyloides) saxorum ( Weinland ) . 



The absence of the flaring outer peristome and the development of 

 the axial ribs into strong denticles, as well as entirely different shape, 

 easily differentiate this from typical Colobostylus, a Jamaican group 

 with which it appears most nearly affined. 



