HISPANIOLAN AND BAHAMAN ANNULARUDAE 215 



of Little Cayman that it seems possible that Maynard got his labels or 

 shells mixed, and that this is really from some of the Cayman group. It 

 differs from C. parvicaymanense by the more compact form, the sutures 

 being less impressed, and by the noticeably coarser sculpture. It was re- 

 ceived from Mr. Maynard in 1897." 



Comparing specimens received from Dr. Pilsbry with the large 

 series of specimens I collected on Little Cayman Island leaves no doubt 

 about its being Chondropoma (Chondropoma) parvicaymanense Pilsbry. 

 Maynard made extensive collections on New Providence and also on 

 Little Cayman, and through some unfortunate slip wrote Nassau, New 

 Providence, when he should have stated Little Cayman. 



The two names having the same date, I deem it best to suggest the 

 suppression of Chondropoma (Chondropoma) soror Pilsbry. 



Subfamily Rhytidopominae Henderson and Bartsch 



1920. Rhytidopominae Henderson and Bartsch, Proc. U. S. Nat. Mus., vol. 58, 

 pp. 64-65. 



Shell ranging from elongate-conic through ovate to turbinate. Axial 

 ribs are always present; they may vary from mere threads to lamellar; 

 they may terminate simply; they may become expanded at the summit 

 into broad denticles or even fused there into hollow cusps or tufts. 

 Spiral threads may be present on spire, base, and umbilicus, or in the 

 umbilicus only, or they may be even entirely absent. The last whorl may 

 be adnate or solute, and the umbilicus may be open or closed. The oper- 

 culum has as a basis a chondroid plate composed of several whorls, the 

 outer surface of which bears numerous, retractively slanting, raised 

 lamellae, which vary greatly in strength in the different genera. They 

 may extend completely across each whorl or they cover only a part of it, 

 as in Opisthosiphon. These lamellae may or may not be fused on their 

 inner and outer termination. They may be rather distantly spaced or 

 they may be almost fused at their edge. Special devices for breathing 

 when the operculum closes the shell may be present or absent. They 

 show an enormous range of specialized development, which will be dis- 

 cussed under each genus. 



Type genus : Rhytidopoma Sykes. 



KEY TO THE BAHAMAN GENERA OF THE SUBFAMILY RHYTIDOPOMINAE 



Siphon present Opisthosiphon 



Siphon absent Colonina 



Genus OPISTHOSIPHON Dall 



1905. Opisthosiphon Dall, Proc. Malac. Soc. London, vol. 6, p. 209, March. 

 1905. Opisthosolen Dall, The Bahama Islands, Geogr. Soc. Baltimore, p. 42, May. 



The shell varies from broadly ovate through elongate-ovate to cylin- 

 droconic. The nuclear whorls are microscopically granulose. The early 

 postnuclear turns may be solute or appressed to the preceding whorl. 



