BIVALVES.._SPONDYLUS. 44 
SPONDYLUS.—Tuorny OvsterR or ARTICHOKE. 
DESCRIPTION OF PLATE XI. 
Diy. I.---Fam. 1. Fig. 1. S. gedaropus.---Fig. 4. variety. 
Dw. II.---Fam., 1. Fig. 3. S. anacanthus. Fam. 2. Fig. 2. §. plicatus. 
Shell hard, solid, with unequal valves; one of the valves convex, the 
other rather flat: hinge with two recurved teeth separated by a 
small hollow. 
THIS genus, though presenting innumerable varieties, 
contains only ten distinct species, and these, from 
their extreme irregularity of formation, and great simi- 
larity of appearance, may often be confounded with each 
other. 
The most striking character of the Spondylus is, that 
its valves, which resemble those of the common oyster, 
have their outsides covered with longitudinal rows of 
erect spines or ramifications. The spines are usually 
round, and terminate ina point; the ramifications or 
branchings, on the contrary, are flat, and have jagged 
and patulous extremities. These peculiarities form the 
distinctions of the two families of the first division. 
Many species possessing these characters are also con- 
centrically plaited on the lower valve. The second 
division is distinguished by its species being longitudi- 
nally striated or plaited. 
The hinge is furnished with two recurved teeth, which 
are very strong and articulate, and separated by a small 
but deep hollow; the inner margin is usually crenulat- 
ed, and highly colored with orange or purple. The 
lower valve generally protrudes much beyond the upper, 
