68 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 58. 



Opisthosiphon (Opisthosiphona) protractus Torre and Henderson Eastern Cuba. 



Opisthosiphon (Opisthosiphona) judacensis Torre and Henderson Eastern Cuba. 



Opisthosiphon (Opisthosiphona) detectus Torre and Henderson Eastern Cuba. 



Opisthosiphon (Opisthosiphona) ohiectus Torre and Henderson Eastern Cuba. 



Descriptions of the last thirteen forms are now going through press. 

 The group of Opisthosip'h.ona dalli: 

 Opisthosiphon (Opisthosiphona) dalli Torre and Henderson Eastern Cuba. 



Subgenus OPISTHOSIPHON Dall. 

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

 Shell elongate-conic, marked by axial and spiral threads on base 

 and spire. External breathing siphon present at the posterior 

 angle. Operculum typically Parachondroid. 



Type of the subgenus. — Cyclostoma lahamense Shuttleworth. 

 The following species are now referred to this subgenus : 



Cyclostoma bahamense Shuttleworth Bahamas. 



Cyclostoma sculptum (Gundlach) Pfeiffer ■. Eastern Cuba. 



Cyclostoma echinatum (Gundlach) Pfeiffer Eastern Cuba. 



Genus XENOPOMA Crosse. 



1890. XenopoTna Crosse, Journ. Conchyl., vol. 38, p. 282. 

 Shell elongate-conic; the last part of the last whorl is detached and 

 deflected considerably below the preceding turn. The sculpture con- 

 sists of widely spaced ribs which bear strong hollow cusplike tubercles 

 at their intersections with the obsolete spiral cords. In addition to 

 this, fine wavy axial threads occur between the cusped ribs. Peri- 

 stome reflected, widely expanded and fluted. Operculum marked by 

 retractively curved ribs, which do not extend across the entire width 

 of the whorls. The inner border of these ribs is fused to form a 

 lamella, which is a little higher than the ribs. The outer border of the 

 ribs become fused to form an enormously developed lamella in the 

 last turn, which is reflected domelike inward over the operculum and 

 almost completely covers it. This reflected lamella bears fuie cor- 

 rugations on its surface. The edge of the operculum is concave. 

 Type of the genus. — Choanopoma hystrix (Wright) Pfeiffer. 

 The following species are now referred to this genus: 



Choanopoma hystrix (Wright) Pfeiffer Eastern Cuba. 



Choanopoma humboldtiana Pfeiffer Eastern Cuba. 



Genus RHYTIDOPOMA Sykes. 



1901. Rhytidopoma Sykes, Journ. Malac, vol. 8, p. 60. 



Shell elongate-conic, axial riblets and spiral threads present in all 



the Imown species; the axial sculpture is usually stronger than the 



spiral. A recurved breathing siphon is present a little behind the 



peristome at the junction of the parietal and outer wall. Operculum 



