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CHAMIDAE 391
I to I K Inches In length, oval to circular, moderately inflated. Exterior
dull-white with numerous, crowded, rather distinct, but small, concentric
threads. Lunule of right valve like a small, depressed, lanceolate shield which
fits snugly into a similarly shaped recess in the left valve. A common Httoral
species in southern California and down to 78 fathoms. Do not confuse with
large specimens of Diplodonta.
Subgenus Ctena Morch i860
Codakia orbicidata Montagu Dwarf Tiger Lucina
North Carolina to the south half of Florida and the West Indies.
Plate 30I
I inch or less in length, very similar to orbicularis^ but with a large,
elongate lunule in front of the beaks (instead of small and heart-shaped), and
with stronger, less numerous, commonly divaricate ribs which are noticeable
right up to the ends of the beaks. This species is much fatter and never has
pink coloring inside. Common in sand from low water to 100 fathoms.
The form filiata Dall has finer sculpturing much like orbicidaris, is often
yellowish in color, but can be readily distinguished from the latter by its
elongate lunule. Common in the Gulf of Mexico.
Genus Divaricella von Martens 1880
Divaricella quadrisidcata Orbigny Cross-hatched Lucina
Plate 30m
Massachusetts to south half of Florida and the West Indies.
/4 to I inch in length, almost circular, moderately inflated, and glossy-
white in color. Sculpture of fine, criss-cross or divaricate, impressed lines.
Inner margin minutely impressed. A very common species washed ashore on
sandy beaches. It is used extensively in the shellcraft business. D. dentata
Wood from the West Indies is very similar, but its inner margin is smooth.
Family CHAMIDAE
a. Shell equivalve, with a distinct lunule; radial rows of spines ....
Echinochama
aa. Shell very Inequivalve; no lunule:
b. Umbones turning from right to left; attached by left valve Chama
bb. Umbones turning from left to right; attached by the right valve
Pseudochama