ACEPHALA. 399 
Length an inch and a half; height three-fourths of an inch. 
A single specimen, with part of the animal, was found in a sandy 
cove, in the Bay of Rio Janeiro. 
Its elongated, leguminous form, and its large size, plainly charac- 
terize it. Inthe specimen examined there is a deep strangulation 
near the anterior end, from the ventral margin half way to the beaks ; 
but it is probably accidental, as the early stages of growth show no 
traces of it. It is the only species of the genus ever found in tropical 
seas. 
Figures 510, 510, 5104, lateral, internal, and dorsal views of the 
shell. 
Saxipomus Nurratii (Conrap), Journ. Acad. Nat. Sc., vil. 249, 
pl. 19, f. 12. 
Found at the Straits of De Fuca, much larger than described by 
Conrad, viz., three and a half inches long, and two and a half high. 
In the young state, it is invested with a fawn-coloured epidermis. 
AMPHIDESMA CROCEUM (Gould). 
Testa maxima, crassa, calcarea, inequivalvis, subcircularts, posticé hian- 
tulu et sub-truncata, liris concentricis reflexis interdum divaricatis 
arata, radiatim striata ; umbonibus sub-medianis, eminentibus, acutts, 
contiguis: intus crocea: cardo validus, fovea ligamental ampla, pro- 
funda; dentibus rosaceis. 
Amphidesma croceum, Goutp; Proceed. Boston Soc. Nat. Hist., 11. 
218. May 1850. Expedition Shells, 78. 
SHELL large and ponderous, externally of a dead. dingy white, in- 
equilateral, very inequivalve, the right valve twice as convex as the 
left, nearly circular; surface concentrically marked with delicate, ir- 
regular, sometimes divaricate, somewhat reflex, concentric wrinkles, 
more conspicuous at the ends; these are traversed by obsolete, un- 
