290 



DESCRIPTION OF A COLLECTION OF FOSSILS, 



Locality. From the coal mine of Pariatambo. Liassic. 



Remarks. The finest bivalve from this rich and interesting locality. The 

 genus has been usually considered as characteristic of the Trias, all of the species 

 in d'Orbigny's Prodrome being placed in his two stages— 5 and 6. But here we 

 have it associated with Crassatella and with Ammonites, one species of which is 

 only doubtfully separated from a known Jurassic form, and with a Gyrodes, true 

 somewhat aberrant, but nevertheless belonging to a genus heretofore not known 

 below the Cretaceous. 



PTERIA, Scop. 



Avicula, Brug. 

 P. iNCONSPicuA, n. s., PI. 41, fig. 5. 



Shell small, flattened, very oblique ; beaks terminal ; anterior side sloping so 

 that the most prominent part of the base is directly under the angle of the wing ; 

 posterior side broadly emarginate above and rounded below. Surface marked by 

 fine lines of growth and a few large faint radiations on the most convex part. 



Figure. Twice natural size. 



Locality. With the preceding. 



BARBATIA, Gray. 

 B.? Raimondii, n. s., PI. 41, fig. 6. 



Shell small, narrow, compressed ; beaks one-fourth of the length from the ante- 

 rior end; umbones low and broad; a broad shallow depression runs from the 

 umbones downwards and backwards, reaching the base about a third of the length 

 of the shell from the anterior end; anterior end produced and subraucronate above, 

 sloping inwards below with a broad curve; base broadly and shallowly emarginate 

 just behind a point opposite the umbones, at the termination of the superficial 

 depression; behind this it is broadly but not prominently convex; posterior end 

 rounded, except adjoining the hinge line, where it is slightly emarginate; area 

 long and very narrow ; surface marked by numerous fine radiating ribs, a little 

 broken by lines of growth. 



Figure. Twice natural size. 



Locality. From the coal mine of Pariatambo. 



Eemarks. Externally this shell resembles d'Orbigny's figure of Cucullaa Tocay- 

 mensis (Amer. Merid., PL 21, figs. 1-3), but differs in having a narrower area, less 

 prominent beaks, and in being of an entirely different form posteriorly. 



TRIGONARCA, Con. 



T. Orbignyana, n. s., PI. 41, fig. 1, 7a, 8, 8a. 



Shell very large, triangular ; beaks placed about a third of the length from the 



