52 Marine Shells of the Western Coast of Florida 



Some species make a nidus from fragments of debris entangled 

 by byssal threads, and others form cavities in wood or coral. The 

 family is byssiferous. 



The shells are equi valve, longest from umbonal region to oppo- 

 site margm; not auriculate; ineqiulateral with sharp umbos. There 

 is a linear hinge ligament, either marginal or partly internal; teeth 

 are absent or feeble; impressions of two adductor muscles — the 

 anterior small, the posterior large and indistinct. Pallial line almost 

 always simple. Interior of valves polished but not nacreous and 

 often of a purple color. The ventral border gapes for passage of a 

 byssus. All have an epidermis. 



Genus IJKACHIDOIVTES Swainson. 1840 

 Braohidontes^^ recur^ns (Rafinesque) PI. 7, fig. 34 



Alt., 30; length, 40 mm. Color dark purplish; shell strongly 

 and obliquely upcurved; umbos anterior, acute, terminal; hinge 

 margin concave, slightly sinuous; anterior and ventral margins 

 sharply curved and continuous; posterior margin rounded; valves 

 finely and closely ribbed; umbos smooth; interior dark purple, 

 nacreous; margins finely crenate with byssal sinus. 



Common in shallow water, often among roots of mangrove 

 trees. 



Brachidontes exustus^* (Linne) PI. 7, fig. 35 



Alt., 10; length, 28 mm. Shell color bluish gray with bright 

 brown; epidermis thin, brown; surface finely ribbed; shell oblique, 

 inflated below hinge margin which is short and straight; ventral 

 margin long, almost straight; interior purple, nacreous, color pale 

 about borders; margins crenate. 



Common on the beach attached to Atrina and to each other. 

 Dredged in three to six fathoms. 



*■* Lat., brachium, arm; Gr. dontes, teeth. 



^* Lat., exustus, past part, of exurere, to burn up. 



