$65 Dominican Fossils — Maury 201 



fixed by the left valve and the area of attachment is small. 

 Locality. — (Exp'd '16) Zone H, Rio Cana at Caimito. 



Genus Echinochama Fischer 



Echinochama antiquata Dall 

 Plate 33, Figure 10 



Chama arcinella Moore, Quart. Jour. Geol. Soc, vol. 9, p. 130, 1853. 



Not of Linne. 

 Chama arcinella Guppy, Id., vol. 22, p. 294, 1866. 



Chama arcinella Gabb, Trans. Amer. Phil. Soc, vol. 15, p. 251, 1873. 

 Chama arcinella Guppy, Geol. Mag. London, vol. ii, p. 442, 1874; 



Quart. Jour. Geol. Soc, vol. 32, p. 531, 1876. 

 Echinochama antiquata Dall, Trans. Wagner Inst. Sci., vol. 3, pt. 6, 



pp. 1404, 1586, pi. 54, fig. 9, 1903. 



A number of our specimens agree very well with Dr. D all's 

 figure of the Bowden shell. They differ markedly from the re- 

 cent E. arcinella Linne, which is living on the Monte Cristi 

 beach, in their less prominent ribs and the more squamose and 

 the less spiny surface. The ribs in the fossil, ancestral, shell 

 tend to become obsolete over the posterior slope. Four valves 

 average 16 ribs which lie chiefly on the anterior two-thirds of 

 the shell. Length 48, height 45, of type length 50, height 48 mm. 



Locality. — (Exp'd '16) Bluff 1, Cercado de Mao. (Large, 

 fine shells). 



Echinochama antiquata variety yaquensis, n. var. 

 Plate 33, Figures 11, 12 



Themajorit}^ of our Echinochamas constitute a well marked 

 variety differing from the typical in several respects. Fifteen 

 valves average only six ribs each, the ribs are distinct and near- 

 ly equally spaced; the shell is smaller and the height somewhat 

 greater than the length, which is reversed in the typical. Thus 

 different valves of the variety measure 38 in length, 40 in height; 

 36X38; 35X37 mm. The variety is especially prevalent in the 

 Gurabo clays. 



Localities. — (Exp'd' 16) Base of limestone capping Zone A, 



