no STUDIES IN GEOLOGY, No. 3 



ensis; it is more equilateral, and has the furrowed umbonal 

 slope not present in the Panama form. If Toula's total 

 thickness of 38 mm. is correct, gatunensis is much more 

 inflated than charanensis, which could not be greater than 

 16 to 1 8 mm. in total diameter. It is also much like A. 

 inequilateris Guppy, 110 but the ribs lack, apparently, the 

 nodes of Guppy's figure (forms from the Bowden beds of 

 Jamaica do not have nodes as prominent) , the beaks are not 

 as sharply conical in shape, and the furrow in the umbonal 

 slope of charanensis is not present in inequilateris. A. dari- 

 ensis Br. & Pils. 111 another form from the Gatun beds, has a 

 more fully curved anterior margin, and the ventral margin 

 does not descend posteriorly ; its ribs are divided by a groove 

 and it is not so fully produced posteriorly as is charonensis. 

 Lower Zorrkos. West side of hill between Quebradas 

 Heath and Charon. 



Area (Scapharca) hispaniolana Maury (?) 



Scapharca hispaniolana Maury, Bull. Amer. Pal., vol. 5, No. 29, 

 p. 176, pi. 30, figs. 9, 10, 1917. 



Shell high, short, cuneiform, inflated. Anterior margin 

 absent in specimen. Ventral margin straight, apparently 

 nearly parallel to the hinge-line; posterior margin truncate, 

 forming slightly less than a right angle with the ventral 

 margin, and an angle of 130 with the hinge-line. Umbones 

 prominent, narrow, incurved; umbonal slope flattened, with 

 decided right-angled keel posteriorly. Ribs, 20-22 in num- 

 ber, square in cross-section, with interspaces equal in width 

 to a trifle wider than the ribs ; concentric growth-lines more 

 distinct in interspaces than on the ribs. Ribs nodulose, 

 giving quadrisulcate appearance to the shell similar to that 



""Quart. Jour. Geol. Soc. Lond., vol. 22, pp. 293-294, pi. 28, 

 fig. 2, 1866. 



111 Proc. Acacl. Nat. Sci. Phila., vol. 63, p. 362, pi. 22, fig. 10, 

 1911. 



