HISPANIOLAN AND BAHAMAN ANNULARIIDAE 



223 



rounded. Base short, well rounded, marked by six slender spiral threads 

 and two heavier ones near the umbilical chink. Aperture broadly oval; 

 peristome double, the outer broadly expanded, deeply notched on the 

 inner lip, and reflected posterior to the notch over the umbilicus which 

 it completely covers; on the parietal wall it is adnate to the preceding 

 turn; there is a moderately strong auricle embracing the siphon; inner 

 peristome slightly exserted and slightly reflected. Operculum typically 

 opisthosiphonid. 



The type (U.S.N. M. No. 536844) was collected by C. C. Allen at 

 Nicholas Town, Andros Island, Bahamas. It has a little over 3 whorls 

 and measures : Length, 7.8 mm. ; greater diameter, 4.5 mm. ; lesser di- 

 ameter, 3.6 mm. 



Two topotypes (U.S.N.M. No. 359897) yield the following additional 

 measurements : 



This species is nearest related to Opisthosiphon (Opisthosiphon) 

 alleni, from which it may at once be distinguished by its much smaller 



size. 



OPISTHOSIPHON (OPISTHOSIPHON) A1.LBNI, new species 



Shell rather large, elongate-conic, ranging from flesh-color to pale 

 brown. Nuclear whorls decollated in all our specimens. Postnuclear 

 whorls strongly rounded and marked by retractively curved, slender 

 axial riblets. Some of these become expanded at the summit and en- 

 larged to form hollow cusps. There are usually one or more unexpanded 

 riblets between these cusps. The spiral sculpture consists of weak threads. 

 Suture slightly channeled. Periphery well rounded. Base moderately 

 long, well rounded, and marked by the continuation of the axial rib and 

 spiral threads, a few of which are apparent also on the exposed um- 

 bilical wall. Aperture broadly oval; peristome double, the outer broadly 

 expanded, a little wider on the inner and parietal lip than on the outer 

 and basal, notched on the middle of the inner lip. Posterior to the notch, 

 the inner lip is reflected over the umbilicus, which it completely covers. 

 The outer peristome is marked by slender concentric lamina and is 

 slightly auriculated at the posterior angle, where it is rendered irregular 

 by the siphon; the inner peristome is slightly exserted and slightly ex- 

 panded. Operculum typically opisthosiphonid. 



This species occupies the islands of New Providence and Eleuthera. 

 I am recognizing two subspecies, which the following key will help to 

 differentiate : 



