- ."^10 - 



groove and 'iie prominent median rib is slip'litly raised. 'i'racGS 

 of reddish brown ooloration are visible. ,,.,. .'..^. l..;'-pvT-,r sixrface 

 of one of the valves. 



E. arcinella li. '• fl) o?oiirs in the 'Jest Indian waters 



(1). Linnaeus, Syst. Hat., e"^. IS, v, 11?9, 1757; Reeve, Oonoh. 

 Icon., vol. 4, -'^1. 5, "^■~. rea, b. 



in depths up to twenty-six fathoms and is also fo^md in tbe Oal- 

 oosahatchie aiid V.'acoainaw Pliocene. In a:''diti'^n to the differences 

 discussed above, arcinella has fewer, broader :•' "^ eh larg- 



er spines and the ventral margin is decidedly affected by the 

 ribs. T'^e yoimg of antiouata have f ewi r ribs than the adult and 

 relatively longer spines, so that they more closely resemble 

 the recent snecies. It is an interesting fact that, as mention- 

 ed above, the 3ov;den form is more closely related to the Lovver 

 Oalifornian E. calif omica Call (2) than to the recent V.'est Indi- 



(-). 



an form. 



The Santo Domlnp^ian s-necimons have in general less promi- 

 nent radiale ''— entire t; iu-;ace iwjre deeply pit'i'e-. 



It £should be stated that Iiall'c figure does not present the 

 shell in its -oro-er -oosition. 



