CEIUON. 179 



Subdivisions of Cerion. 



I. Parietal lamella short, situated in the angle between the colu- 

 mella and parietal wall; axial lamella below it; whorls very 

 short. PI. 47, fig. 38. Subgenus CERION. 



II. Axial and parietal lamellae present, the latter near the middle of 



the parietal wall, simple and short, usually not penetrating over 



one-third of a whorl. PI. 47, figs. 37, 40. Subgenus STROPHIOPS. 



III. Axial and parietal lamella present, the latter very long and 



doubled, or short and interrupted, with an accessory denticle ; 



rarely obsolete. PI. 47, fig. 39. Subgenus DIACERION. 



IV. Axial and parietal lamella or teeth wanting. 



Subgenus EOSTROPHIA. 



NOTE Some forms of Diacerion in which the parietal armature 

 is degenerate or incipient, have the structure of Strophiops. 

 The species are herein classified in fifteen groups, as follows : 



Subgenus CERION (typical forms). 



1. Group of C. uva. Curacao. 



Subganus STROPHIOPS Dall. 



2. Group of C. pannosum. Little Cayman, Cayman Brae. 



3. Group of C. crassilabris. 



Species of Guiana. 



Species of St. Croix, Porto Rico and Haiti. 



Species of Grand Cayman. 



4. Group of C. cyclostomum. Cuba. 



5. Group of C. maritimum. Cuba. 



6. Group of C. scalarium. Cuba, Bahamas. 

 Y. Group of C. mumia. Cuba. 



8. Group of C. regina. Bahamas. 



9. Group of C. gubernatoria. Bahamas. 

 10. Group of C. album. Bahamas. 



II. Group of C. glans. Bahamas. 



12. Group of C. martensi. Bahamas. 



Subgenus DIACERION Dall. 



13. Group of C. rubicundum. Inagua. 



14. Group of C. striatellum. Eastern Cuba. 



Subgenus EOSTROPHIA Dall. 



15. Group of C. anodonta. Tampa silex beds (Oligocene). 



