232 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
gether, internally. Margin straight, without perceptible curve or sinu- 
ation; slightly angular at the anterior edge, giving a very slight appearance 
of truncation. Valves nearly equally inflated. Beak of the neural valve 
small, recurved, obliquely truncated. Foramen small, entire, apical; the 
carination of the edge of the false area encroaches on the perforation in 
a triangular point on each side. False area small, narrow, smooth, roundly 
carinated at the edge. Deltidia very short and wide, united. Long., 1.9 
inch; lat., 1.6 inch; diameter, 1.2 inch; height of neural apex above the 
opposite umbo, .15 of an inch; diameter of foramen, 1 inch. Peduncle 
very short and stout. Teeth of the neural valve short and stout. Hinge 
line very slightly emarginate (for the cardinal process) beneath the umbo, 
otherwise gently rounded. Teeth supported by shelly plates beneath the 
hinge line. Cavity of the apex infundibulate. Out of this cavity proceed 
two strong, but not prominent, ridges, which radiate toward angles of the 
anterior edge of the margin, but become evanescent before passing the 
central third of the shell. Between these ridges are two others, one on 
each side, close to the median line, shorter and less prominent than the 
first. There are faint indications of others outside the two first mentioned, 
and these ridges, except the first two, are variable in different individuals. 
Cardinal process very conspicuous. Cardinal plate broadly pentagonal, 
centrally depressed. Septum not prominent, diminishing in height from 
the edge of the plate forward, and not extending more than half the length 
of the shell; point of attachment of the apophyses quite close to the plate. 
Apophyses start from the anterior angles of the plate and give off two 
curved slender crura; the haemal processes are very slender; septal 
processes still more so; reflected portion quite broad, somewhat angulated 
behind, the inner edge of the haemal processes at the point from which 
the septal processes are extended to the septum. There is no flat top to 
the latter, such as is seen in Ter. dorsata, effusa et caurina. (Dali.) 
Type in N. & N. M., No. 19395. Type locality, off Catalina Island, 
in 80 fathoms. 
Range. Known only from the type locality. 
Genus MARCIA H. & A. Adams, 1857. 
Shell with the surface of the valves smooth. (H. & A. Adams.) 
Shell large, subquadrate, concentrically lamellose and striated, without 
radial sculpture, and a dull, earthy surface; internal margin smooth; 
pallial sinus small, angular, free; hinge with three left and four right 
cardinals, the middle ones larger and grooved above. (Dali.) 
Distribution. Alaska to California. 
Tertiary. North America. 
Type. Venus exalbida Dillwyn. 
Subgenus Mania Gray, 1849. 
