330 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



KEY TO THE GENUS CERITHIOPSIS. 1 



Shell with varices excelsa. 



Shell without varices. 



Spiral cords between the sutures three. 

 Spiral cord at summit equal to the others in strength. 

 Sutures strongly channeled. 



Shell of medium size, less than 6.5 mm. long fatua. 



Shell minute; adult less than 4 mm. long. 

 Base with two spiral cords. 



Shell elongate-conic oxys. 



Shell elongate-ovate curtata. 



Base with more than two spiral cords. 



Spiral cords of base three cerea. 



Spiral cords of base nine sorex. 



Sutures not channeled. 

 Whorls shouldered at the summit 

 Base with strong spiral cords. 

 Shell large; adult more than 7 mm. long. 

 Spaces inclosed between axial ribs and spiral cords on the spire, large 

 squarish pits. 



Base with a strong keel next to peripheral keel fossilis. 



Base with no strong keel next to peripheral keel gloriosa. 



Spaces inclosed between axial ribs and spiral cords on the spire, small 

 round pits. 

 Peripheral keel completely exposed in the suture in adult shells, 



columna. 



Peripheral keel never completely exposed in the suture in adult 

 shell. 



Basal cords three, strong cosmia. 



Basal cord single, feeble " carpenteri. 



Shell smaller. 

 Adult between 3 and 5 mm. long. 

 Basal cord broad and round. 



Axial ribs on last whorl about 32 pedroana. 



Axial ribs on last whorl about 20 tuber culoides. 



Basal cords sublamellar. 



Adult less than 3 mm. long infrequens. 



Shell stout pupiformis. 



Shell slender abreojosensis. 



Base with feeble sculpture only. 

 Basal fasciole present. 

 Base with a single fasciole (encircling the columella) only. 



Shell broadly elongate-conic paramoea. 



Shell slender elongate-conic necropolitana. 



Base with more cords than a single fasciole arnoldi. 



Basal fasciole absent. 



Whorls not shouldered at the summit magellcmica cesta. 



Spiral cord at summit weaker than the rest. 

 Sutures strongly channeled. 

 Shell robust. 

 Basal keels strong berryi. 



1 Since so many of the species under discussion lack the nucleus, it was deemed advisable to treat the 

 genus as a unit and ignore the subgeneric division in this key, by utilizing characters present on the post- 

 nuclear whorls only. 



