Page:American Seashells (1954).djvu/473

Rh 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 Plate 30I North Carolina to the south half of Florida and the West Indies. 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