The Pyramid Shells. Obelisk Shells 



characteristic cross ridges on its ten flat whorls, is a rich brown 

 on the outside. Length, ^ inch. 

 Habitat. — Cahfornia. 



Genus ODOSTOMIA, Flam. 



Even smaller than the preceding genus, which it resembles 

 in form, in most cases a trifle stouter and with a tooth-like fold, 

 always, on the curved columella. Animal lives on slimy excreta 

 of other mollusks, or on polyps and sponges of small size. The 

 shells are white and lack cross-sculpture. 



O. impressa, Say, is regularly conical but slender, its spire 

 wound with close, grooved lines. The lip flares around an oval 

 aperture. Length, J inch. 



Habitat. — Massachusetts Bay to West Indies, West Florida. 



173 



