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 



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 



