THE NAUTILUS. 89 



c. With operculum of Chondropoma. 



Chondropoma egregium Gundl. Pinar del Rio, Cuba. 



d. With operculum unknown. 



Licina percraasa Wright. Pinar del Rio. 



Third. With perforation not penetrating to exterior of whorl 

 but connecting with an internal air space 

 which is situated in the upper angle of the 

 whorl and extends back from the aperture for 

 a considerable distance. In some specimens 

 it may be traced for over two whorls. 

 Rhytidopoma bilabiatum Orb. Pinar del Rio. 



The first group has a restricted geographical distribution ex- 

 tending from the Bahamas through central Cuba to the Isle of 

 Pines. Choanopoma uncinatiim Arango while possessing the 

 typical Opisthosiphon breathing tube has the very different 

 operculum of a Choanopoma. It therefore cannot be included 

 in Opisthosiphon, and until a careful study of the animal shows 

 its true relationships may be retained as an aberrant Choano- 

 poma. 



The second group is confined to western Cuba and while con- 

 taining species with very different opercula, and therefore a 

 group of apparently no systematic value, is nevertheless inter- 

 esting, in that it is confined almost entirely to Pinar del Rio, 

 and entirely to western Cuba. 



The third group, of which I have seen but one species, is of 

 interest because of the fact that in this case the perforation and 

 internal tube appear to be of no practical value; for, though one 

 might be led to expect that at certain stages of growth, com- 

 munication to the exterior might exist through the external 

 sutural flanges, I have been unable to find any structural evi- 

 dence of such connection. 



It would appear from the above that if the breathing tube is 

 to be considered of value as a generic character together with 

 the operculum, as in the case of Opisthosiphon, Choanopoma 

 uncinatum Arango would have to be placed in a new genus, the 

 operculum being very different from that of Opisthosiphon; 

 while the breathing tube, having been considered of sufficient 



