44 Marine Shells of the Western Coast of Florida 



shorter, than the flattened upper valve. The umbo of the left valve 

 is lengthened and strong and may be directed either forward or 

 backward. Umbo of right valve is short. Both umbos have a central 

 channel in their approximate surfaces for ligamentary attachment. 

 The surface of the lower valve is lamellate and folded; that of the 

 upper valve is lamellate, ribbed, and often spiny. Margin more or 

 less deeply serrate; interior of valves smooth with a central spot of 

 deep purple and a prominent subcentral muscle scar. 



Oysters are preyed upon by carnivorous mollusks, Busycon, 

 Melongena, Fasciolaria, and many are eaten by sheepshead from the 

 oyster bars, mangrove roots and pilings. 



Family SPONDYLIDAE 



The two American East Coast genera of the family Spondylidae 

 are distributed in warm waters southward from North Carolina, 

 through the West Indies, and in the Gulf of Mexico to Texas. The 

 genus Spondylus includes the thorny oyster, one of the most extra- 

 ordinary of marine shells in its development of protective spines and 

 in brilliancy of color. 



The shells are inequivalve, attached by the right valve which is 

 larger and deeper than the upper left valve. The hinge is of peculiar 

 interest, it is unusually strong and permits only limited separation 

 of the valves; there is a central ligamentary fossette and two cardinal 

 teeth in each valve, the teeth articulate with sockets in the opposite 

 valve. 



Genus SPOJfDYLUS Linne, 1758 

 Spondylus-^' ioterious Reeve PI. 5, fig. 23 



Alt., 70; length, 55 mm. Shell rounded, trigonal, irregular; 

 colored in shades of red and orange; inequivalve; eared; fixed by 

 a triangular area at umbonal extremity of right valve, the surface of 

 this triangular area is white with a deep longitudinal slit for the 

 lodgment of a portion of the elastic ligament. The fixed valve is 

 normally deeper than its fellow, but is frequently flattened in whole 

 or in part by pressure from adjacent reef structures; its surface 



'^ Gr., spondylus, vertebra; ictcrikos, jaundice. 



