- l(-6 - 



are inflated, with more or less rounded ribs separatef] by narrovrer 

 interspaces. Tumbers of the la. st group somewhat resemble 0. peot- 

 inata (Gmelin) (1), bxit differ by their higher umbones, narrower 



(1). Srst. ITat., p..l?lJ?, 1792. 



ribs and interspaces. 



G, canal is Brovna and Pilsbry (2), described from Gatun, 



(2). Proc. Acad, Hat. Sci., Philadelphia, vol. 63, p. 364, pi, 

 28, fi?. 10, 1911. 



Panama, is more inflated, v/ith rounde' ribs, v:h ch may, however, 

 be subangular. 



Ocourrence .- Upper Oligooene.- Santo .Dominp-o (Sowerby, 1050; 

 Gabb, 1873; Gup^y, 1874, 1876). Gumana, Venezuela (Guppy, 1874). 

 Gatun formation, Panama fBro?m and Pilsbry, 1911). Lov/er i'^iocene : 



Bowden beds, ^x-ien, Jamaica. (GuDoy, 1874; 1875; Bsll, 1808). 



