176 Studies in Geology, No. 3 



Comparison with these species to which the other Cimeo- 

 corbulas of the Zorritos have been likened will show similar- 

 ities, but none is as clear as the relationships named above. 

 C. spheuia Dall -^^ from the Chipola of Florida, is close, but 

 is less clearly triangular in shape, lacks the l^evelled carina, 

 and has slightly coarser sculpture. In sphenia the carina 

 curves downward as it approaches the ventral margin ; in 

 bravoana it curves upward. It is also similar superficially to 

 C. coijuifica Maury '°* of the Lower Miocene of Santo Do- 

 mingo. The sculpture does not curve ventrally in bravoana 

 as it does in caiiiiitica; the bevelled carina is again a point 

 of difference, and the anterior margin of caimitica is more 

 completely rounded. This species departs a bit more widely 

 from those European forms to which C. acutirosfra is com- 

 pared. It is named in honor of Dr. Jose Bravo, chief of the 

 Cuerpo de Ingenieros de Peru. 



Lower Zorritos. Between Quebradas Heath and Charon. 



Corbula (Cuncocorbula) acutirosfra n. sp. 



Plate X — Figs. 18, 19. 



Shell of medium size, rostrally truncate, triangular. An- 

 terior margin rounded ; ventral margin elliptical ; posterior 

 margin sharply angulate. Beaks not prominent, anterior in 

 ])osition, proximate, somewhat flattened above. Anterior 

 surface rounded ; mesial surface flat longitudinally and 

 curved vertically. Posterior surface concave, separated from 

 the rest of the shell by a very sharp carina which is bowed, 

 its concave side upward. Sculpture of fine and regularly 

 graven concentric lines which limit somewdiat broader ribs. 

 On the concave surface behind the sharp carina the lines are 

 broader and stronger, recurving toward the hinge, and the 

 elevated ribs are thin and cusp-like. There is a second faint 

 carina near the postero-dorsal margin. The valves are 



-""rrans. Wag. Inst., vol. 3, pt. 4, p. 847, pi. 36, fig. 10, 1898. 



■■"' Bull. Amer. Pal., vol. 5, No. 29, p. 233, pi. 39, figs. 18, 19, 1917. 



