Spondylidae 45 



bears many foliate lamellae. The upper valve is radiately ribbed; 

 prominent ribs alternating with delicately ribbed interspaces which 

 show slightly stronger ribs in the center. The primary ribs bear 

 many sharp, spmose processes; the mtermediate ribs show a similar 

 tendency, often expressed as a beading. Margin rounded. Hinge of 

 two strong cardinal teeth in each valve and a powerful elastic liga- 

 ment; interior of valves smooth, pink or lavender tinted, margins 

 red-bordered and crenate. Single muscle scar; simple pallial line. 



On reefs in five or more fathoms. Best taken by use of a tangle. 



Spondylus americanas Hermann Frontispiece 



Alt., 112; length, 95; thickness, 65 mm. Shell suborbicular; 

 eared, narrowed trigonally near the umbo of the upper or right 

 valve, which is higher and more inflated than the left. Basic 

 color white, with yellow, orange or shades of red near the umbos; 

 less likely to be affixed than Spondylus ictericus. Both valves have six 

 to eight radial ribs with long, curved, palmate spines. Between these 

 heavy ribs are three or four finer ribs with short, pointed spines. 

 Umbo of lower valve widely extended beyond upper valve, showing a 

 triangular, smooth, white area, split in the center, from which ex- 

 tends the elastic ligament which controls the hinge. Each valve has 

 two heavy, cardinal teeth and two corresponding sockets. 



Inside of shell smooth and white, in some instances having a 

 trace of color on the rounded, denticulate margin. One large muscle 

 scar about 30 mm. in diameter. 



Dredged in five or more fathoms. Brought up frequently by 

 the sponge fishermen from Tarpon Springs. 



The Spondylus is usually covered with sponge, which tends to 

 protect the long, delicate spines. The Mediterranean species is said 

 to have been the inspiration for the first mechanical hinge, copied 

 for its perfection and efficiency of construction. 



Genus PLICATULA Lamarck, 1801 

 Plicatula32 gibbosa Lamarck PI. 5, fig. 24 



Alt., 25; length, 24; diam., 10 mm. Shell solid, thick, irregular, 



3- Lat., flicatus, folded, ula, fem. dim.; gibbus, a hump. 



