CLASS PELECYPODA 
81 
beyond which the margin is minutely crenulate; interior bluish perlaceous; 
hinge line behind the beaks slightly rounded and produced, but not quite 
angulate. Longest extension of shell, 12; dimension at right angles to 
this, 8.5; diameter, 7 mm. (Dali.) 
Type in U. S. N. M., Nos. 110464 and 110465. Type locality, Stations 
4782 and 4784 off east end of Attu Island in 57 and 135 fathoms. 
Range. Bering Sea to Sitka, Alaska. 
Crenella rotundata Dali, 1916. 
Proc. U. S. N. M., 52:406. 
Shell small, rounded-quadrate, inflated, with a very thin, dehiscent, 
pale-olive periostracum; beaks central, inconspicuous, with no crenula- 
tions beneath them; sculpture of faint incremental lines and obsolete, 
radial striae near the margin; inner margin very delicately crenulate except 
near the beaks. Length, 4; breadth, 4; diameter, 2 mm. (Dali.) 
Type in U. S. N. M., No. 129305. Type locality, Station 2849 off 
Santa Cruz Island, California. 
Range. Known only from the type locality. 
Crenella divaricata Orbigny, 1846. 
Moll. Cuba, 2:311; pi. 27, figs. 56-59. 
Testa globulosa, subcirculari, albida, radiatim costata; costis trans- 
versim granulosis, in medio divaricatis; latere buccalis brevi rotundato; 
latere anali elongato; umbonibus elevatis, contortis. Diameter, 3 mm. 
(Orbigny.) 
This little shell is not to be distinguished, except by its nearly white 
color, from the young of C. decnssata of the same size. The young 
divaricata is proportionately less inflated and has a more circular outline 
than the full-grown shell. The color is yellowish or nearly white in all 
the specimens I have seen, and the epidermis hardly perceptible. (Dali.) 
Type. Neither the location of the type nor the type locality is known 
to the present writer. 
Range. Santa Barbara Islands to Panama Bay. Also West Indies. 
Family PERIPLOMATID2E. 
Genus PERIPLOMA Schumacher, 1817. 
Shell oval, very inequivalve, inequilateral, slightly nacreous; left valve 
deepest; posterior side very short and contracted; hinge with a narrow, 
oblique, spoon-shaped process in each valve, and a small triangular 
ossicle; an internal rib proceeds from under the hinge to the posterior 
margin; muscular impressions unequal, the anterior long and narrow, the 
