ACEPHALA. 435 
Hinge simple, with a very small cardinal papilla on the right valve. 
Nacre silvery, with livid green cloudings; muscular scars well marked. 
Length an inch and five-eighths ; height seven-eighths of an inch ; 
breadth half an inch. . 
Inhabits Peru. 
This shell appears to be different from any which I find described. 
Its peculiar colour, a dead russet green, with the epidermis remarkably 
corrugated into zigzag loops, may serve to distinguish it. It would 
come under the genus Monocondylea of D’Orbigny. ‘The name first 
applied is pre-occupied. 
Figures 548, 548 a, 548 6, three views of the shell. 
AnoponTa coenata (Gould). 
T. fragils, transversa, oblongo-ovata ; margine dorsal brevi, recto ; 
margine ventrali arcuato ; latere antico rotundato ; latere postico ob- 
lique truncato, ad apicem rotundato ; disco turgido ; epidermide vires- 
cente, nitido; apicibus ante-medianis inconspicuis, undulatis: mar- 
gartta livido-albida. 
Anodon cognata, GouLD ; Proceed. Boston Soc. Nat. Hist., iii. 294. 
Nov. 1850. Expedition Shells, 87. 
SHELL elongate, transversely ovate, thin and fragile, pale yellowish- 
green, more yellow in the young, faintly radiated: beaks at the ante- 
rior third, inconspicuous, wrinkled: disk turgid: dorsal margin short, 
rectilinear: basal margin strongly arcuate, especially behind the mid- 
dle: anterior end narrow, rounded; posteriorly compressed above, 
with a long oblique slope, somewhat nasute: pale leaden within, 
clouded with livid. Cavity of the beaks nearly wanting, the valve 
being almost symmetrically spoon-shaped ; impressions very faint. 
Length three inches; height one inch and a half; breadth one inch. 
Inhabits Nisqually and Vancouver, Oregon. Dr. Foz. 
Resembles small specimens of A. cygnea ; but the dorsal margin is 
