SPHtERIUM. 41 



This is a very distinct species ; I know of no other to which it 

 bears any resemblance ; it is remarlvable for its compressed ap- 

 pearance, and for the depression of its beaks. Tliough pretty 

 widely distributed, it does not seem to be found anywhere in much 



abundance. 



The epidermis of the shell is at times so entirely stained with a 

 darkish substance, that it is with difficulty that its color can be 

 detected. 



1&. SplaSeriiUM occadeiitale, Prime.— Animal not observed. 



Shell oval, small, pellucid, fragile, e^iuilateral, margins 

 rounded ; valves slight, rather convex ; beaks full, round- ^^S- ^4. 



ed, not much raised ; sulcations very fine, hardly visible ; „,,cr^. 



epidermis horn color; cardinal teeth very diminutive; , 

 lateral teeth more distinct. |v ^ 



Long. 0.31 ; Lat. 0.25 ; Diam. 0.18 inches. 

 Hab. North America, in the States of New York, Ver- s. occidentale. 

 mont, Ohio, Michigan, Wisconsin, in the Hell Gate River, 

 Washington Territory, and in Canada. (Cabinets of the Academy of Na- 

 tural Sciences of Philadelphia, Smithsonian Institution, Jay and Prime.) 



Cyclas ovalis (preoc), Prime, Bost. Proc. IV, 1852, 276. 



Sphmrium ovale, Stimpson, Adams, rec. gen. II, 185^, 450. 



Sphcerium occidentale, Prime, Proc. Ac. N. S. Phila. 1860, 295. 



This species is remarkable for its completely oval shape, which 

 renders it quite distinct from all others. It is found not uncom- 

 inonly. Compared with S. partumeium, under which name it 

 has at times been sent to me, it is much smaller, the margins are 

 more rounded, and the beaks are not so much raised. 



11. SpliiBrilini MOUile, Gould.— Animal not observed. 

 Shell rhombic-ovate, inequilateral, moderately compressed; anterior 

 margin truncated, posterior more distended, basal curved ; 

 beaks rounded, inclined towards the front, slightly tumid, ^^S- ^^^ 



separate at apex; sulcations coarse; epidermis delicate, ^..^-^^ 



light brown ; valves strong, interior white ; hinge-margin 

 nearly straight, moderately broad; cardinal teeth single, ^j^^^^ 



distinct ; lateral teeth moderately developed. ^ ^^^^.^ 



Long. 0.50; Lat. 0.37; Diam. 0.25 inches. 

 Hah. North America, at San Pedro, in the State of California. (Cabi- 

 nets of Gould, Smithsonian Institution and Prime.) 



Cyclas nohiUs, Gould, Bost. Proc. V, 1855, 229. Atlas of U. S. Exp. 

 Expedit. pi. 36. 



