390 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



Junctions of axial ribs and spiral cords forming well-rounded tubercles. 



Shell large, unicolor, rusty- white (fossil) armillatum. 



Shell small, wax-yellow, variegated with chestnut, usually with a broad, 

 chestnut, basal band. 



Adult shell more than 6 mm. long purpureum. 



Adult shell less than 5 mm. long decussatum. 



Axial ribs and spiral cords always strong and wider than the spaces inclosed by 

 them. 



Shell very large, with strong intercalated spiral cords ornatissimum. 



Shell smaller, without, or with very weak intercalated spiral cords only. 



Shell dark purplish-brown... Vancouver ense. 



Shell wax-yellow, banded with brown. 



Shell robust, with 25-30 axial ribs on its last whorl munitum. 



Shell smaller, with as many as 40 axial ribs on its last whorl, .m. munitoide. 

 Spiral sculpture, consisting of four strong cords between the sutures, between which 

 intercalated slender cords may occur. 

 Axial ribs becoming obsolete on the last whorls of the adult shell. 

 Summit of the whorls appressed. 

 Intercalated spiral cords absent. 



Shell slender, sculpture weak attenuatum. 



Shell robust, sculpture strong a. boreale. 



Intercalated spiral cords present a. multifilosum. 



Summit of the whorls slopingly shouldered a. latifilosum. 



Axial ribs strong on all the whorls. 



Nodulose spiral cords at the summit less strong than the others. 

 Spiral cords sloping gently anteriorly until fused with the body of the shell; 

 posteriorly they are suddenly truncated. 

 Axial ribs on the last whorl 12-15. 



Shell of 10 post-nuclear whorls 8.1 mm. long asperwm. 



Shell of 10 post-nuclear whorls 7.1 mm. long a. lomaense. 



Axial ribs on the last whorl about 25 subplanatum. 



Nodulose spiral cord at the summit equal to the rest on the last whorl. 

 Adult shell more than 17 mm. long. 



Shell slender ; giganteum. 



Shell stout. 



Intercalated cords when present very feeble casmaliense . 



Intercalated cords always present, at times more than one between the 



strong cords and almost equal to them in strength arnoldi. 



Adult shell less than 13 mm. long. 

 Whorls decidedly overhanging. 



Base well rounded rugatum. 



Base flattened. 



Early post-nuclear whorls with 4 spiral cords larum. 



Early post-nuclear whorls with 2 spiral cords cerralvoense. 



Whorls not overhanging. 



Shell large; adult shell more than 11 mm. long quadrifilatum. 



Shell small; adult shell less than 7 mm. long. 



Whorls shouldered at the summit nicholsi. 



Whorls appressed at the summit. 



Axial ribs on last whorl 15 mexicanum. 



Axial ribs on last whorl 32 nitens. 



