CUBAN ANNULARIIDAE — TOKRE AND BAKTSCH 133 



In conclusion, we wish to express again our thanks and appreciation 

 to all the institutions and individuals aclmowledged in our former 

 paper. Without their continued help this monograph would have 

 been incomplete. 



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 vaiy from mere threads to 

 lamellae; 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 m the umbdicus only, or they may be even entirely 

 absent. The last whorl may be adnate or solute and the mnbilicus 

 may be open or closed. The operculum 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 may cover only a part of it, as in Opistho- 

 siphon. These lamellae may or may not be fused on their inner and 

 outer termuaation. 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 

 discussed under each genus. 



Type genus. — Rhytidopoma Sykes. 



KEY TO THE GENERA OF THE SUBFAMILY RHYTIDOPOMINAE 



Breathing device present. 



Breathing siphon present. 

 Siphon complete. 



Lamellae of the operculum extending completely 



across the whorl Opisthocoelicum 



Lamellae of the operculum not extending completely 

 across the whorl. 



Lamellae of the operculum fused at their inner and 

 outer edge to form a spiral keel. 



Lamellae between the inner and outer keel 



as high as the keels Torrella 



Lamellae between the inner and outer keel 

 not as high as the keels, but concave at 



the free edge Rhytidoponia 



Lamellae of the operculum not fused at their 



outer edge Opisthosiphon 



Siphon incomplete Dallsiphona 



