". . . the shells of several species of the genus Spondylus are distinguished for their variety of form and the brilliant colours with which they are decorated. This makes them much sought after by amateur collectors, and procures for them a high price. The shell of Spondylus is solid and thick, . . . nearly always bristling with spines, forming a very peculiar kind of ornamentation. . . Spondylus regius (Fig. I.) is, perhaps, the most remarkable for its immense spines:
Spondulus radians, Lamarck (Fig. III.) is noted for its elegant form:
Spondylus avicularis (Fig. IV.) shows remarkable inequality in the valves:
Spondylus imperialitis, Chenu (Fig. II.) has long projecting spines, like feet:
and the Scaly Spondylus (S. crassisquama, Fig. V.) is covered with scales arranged like so many roofing tiles:
. . . the genus Spondylus is frequently found firmly rooted to rocks and other submarine bodies, and, oftener still, heaped one upon the other, like herrings in their barrel. These animals belong essentially to the seas of warm countries. We find them, however, occupying considerable space in the Mediterranean, where the S. gaederopus (Fig. VI.) abounds:
The variation in the number and direction of the spines is a striking feature in Spondylus. When the whole lower surface adheres to branches of coral--a very frequent occurrence--they are confined to the upper valve; but when a part only of the valve is so adherent, the whole surface becomes covered." [pp.405-406]Kevin Lampress and Thora Whitehead have written a book titled Spondylus: Spiny Oyster Shells of the World and the Google Booksearch Preview is worth a look to see the color photos on the cover. There is even a Wordpress weblog dedicated to archaeological discussion of the spiny oyster and a very scholarly Spondylous Bibliography has been published there.