284 DESCRIPTION OF A COLLECTION OF FOSSILS, 



form shape and its ribs. From the following it can be distinguished by the fine 

 ribs, smaller size, and less truncated anterior end. Associated with this is a single 

 specimen, somewhat mutilated, so that the shape is not all retained. It has smaller 

 ribs, and shows faint traces of radiating lines. I believe it to be different, but 

 have not material for describing it. Both are left valves. 



C. Ratmondii, n. s., PL 40, fig. 12. 



Shell small, robust, cuneiform ; beak of right valve large, prominent, and invo- 

 lute ; anterior end rounded, truncate, sloping nearly straight and obliquely to the 

 base, where it is narrowly rounded. Base broadly convex ; posterior side concave 

 above, the area joining the surface by a regular curve, and not bounded by a ridge 

 as in the preceding species ; posterior end narrow and produced. Surface marked 

 by large, rounded concentric ribs. , 



Locality. With the two preceding species. 



Remarks. Easily distinguished by its large, coarse ribs, its prominent beak, the 

 nearly straight sloping anterior end, and by the absence of a ridge running from 

 the beaks to the upper part of the posterior end. The most marked species of the 

 three. 



PHOLADOMYA, Sby. 

 P. AusTRALis, n. s., PI. 40, fig. 14. 



Shell small, oblique, very inequilateral, convex ; beaks placed close to the 

 anterior end, large, incurved ; anterior end narrowly rounded ; posterior broad, 

 regularly rounded, and slightly oblique. Surface smooth in advance ; seven radi- 

 ating ribs run from the beaks to the base, their ends occupying almost the entire 

 basal margin; posterior to these the surface is covered with small rounded, con- 

 centric ribs, faint traces of which can be seen between the radiations ; posterior to 

 the beaks and adjoining the cardinal margin, is a small, narrow, cordate area, 

 slightly concave and bounded by a slight angle. 

 Figure. Natural size. 



Locality. Hacienda of Macanga. Cretaceous. 



Remarks. Two suites of specimens, one from near Cajamarca, the other from 

 the province of Huari, have the same size and general form, but show no surface 

 markings. 

 P. Raimondii, n. s., PI. 40, fig.. 15. 



Shell very inequilateral ; beaks placed about a third of the length from the 

 anterior end, which is broadly and regularly rounded; posterior end narrower than 

 the anterior, and produced ; base most prominent directly under the beaks. Sur- 



