222 BULLETIN 192, UNITED STATES NATIONAL MUSEUM 



Subgenus Opisthosiphon Dall 



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



Opisthosiphons with spiral threads on spire, base, and umbilicus. 



Type species: Ctenopoma hahamense Shutthworth = Opisthostphon 

 (Opisthosiphon) haJiamensis (Shuttleworth). 



KEY TO THE BAHAMAN SPECIES OF THE SUBGENUS OPISTHOSIPHON 

 Inner lip of outer peristome notched, posterior portion reflected 



to close umbilicus. • j, i • 



Axial ribs distantly spaced mcholasi 



Axial ribs not distantly spaced • al em 



Inner lip of outer peristome not notched, posterior portion not 

 reflected to close umbilicus. 

 Last whorl solute. 



Axial ribs very distantly spaced mayori 



Axial ribs not very distantly spaced. , 



Last whorl strongly deflected "^"Isi 



Last whorl not strongly deflected. 



Axial ribs very strong androsensis 



Axial ribs weak reticulatus 



Last whorl not solute. 



Spiral sculpture of spire very feeble eleutheraensis 



Spiral sculpture of spire not very feeble. 

 Axial ribs distantly spaced. 



Junctions of the axial ribs and spiral threads 



sharply nodulose turkensis 



Junctions of the axial ribs and spiral threads 



not sharply nodulose vaugham 



Axial ribs not distantly spaced. 



Inner lip of outer peristome very broadly 



expanded bahamensis 



Inner lip of outer peristome not very broadly 

 expanded. 



Shell short and stout phoenicopterus 



Shell not short and stout. _ 



Axial ribs fine and closely spaced goldmgi 



Axial ribs not fine nor closely spaced drewi 



OPISTHOSIPHON (OPISTHOSIPHON) NICHOI.ASI, new species 



Plate 36, Figure 6 

 Shell small, elongate-conic, thin, flesh-colored, with very slender inter- 

 rupted spiral lines of brown, of which three occur between the summit 

 and the suture; the peristome is yellowish white. Nuclear whorls de- 

 collated in all our specimens. Postnuclear whorls inflated, strongly 

 rounded, narrowly shouldered at the summit, marked by very slender, 

 distantly spaced, almost vertical axial riblets, of which 50 occur on the 

 first of the remaining turns and 58 on the rest. The spiral sculpture con- 

 sists of rather strong threads, which equal the riblets in strength and 

 which render these somewhat wavy. Of these six occur on the first and 

 nine on the remaining turns. Suture channeled. Periphery mflated, well 



