31 



CHAP. XIII. 



BIVALVES: 

 SPONDYLUS; Thorny .Oyster, or Artichoke. 



Q. DESCRIBE the peculiarities of this genus 

 of shells. 



A. The shell of the Spondylus is inequivalve 

 and rough. The hinge has two recurved teeth, 

 which are separated by a small hollow, some- 

 times eared. One of the valves is convex and 

 thick, the other flat. 



Q. Does not the Spondylus considerably re- 

 semble the Ostrea in its general appearance ? 



A.- Yes the affinity between them is certainly 

 very great, but the strong and well-defined teeth, 

 which are peculiar to this genus, form distin- 

 guishing characteristics. 



Q. Does not the Spondyli generally attach 

 themselves to rocks ? 



A. They are found on marine rocks, at con- 

 siderable depths in the ocean, from which it is 



