178 APPENDIX E. PALEONTOLOGY. 



FOSSILS OF THE CRETACEOUS PERIOD. 



MOLLUSCA. 



Pecten quadrico status, Sowerby. 

 Palaeontology, PI. 3, fig. 6, and PI—, fig. — . 



Janira quadricostata, D'Orbig. Pal. Frang., Ill, 644, pi. ccccxlvii, 

 fig. 1-7. 



Pecten quadricostatus, F. Roemer, Kreid. Texas, 64, taf. viii, fig. 4, 

 a — c. 



Shell sub-ovate, angulated, convexo-concave. Inferior valve convex, 

 with prominent rounded radiating ribs, crossed by five concentric thread- 

 like strias. Ribs from fifteen to seventeen, of which five are more prom- 

 inent than the others ; smaller ribs disposed in pairs in the intervals 

 between the larger ones. Superior valve slightly concave, with radiating 

 unequal ribs. 



As we have not been able to consult Sowerby's description of Pecten 

 quadricostatus, we refer our fossil to this species on the authority of Dr. 

 F. Roemer, whose figures and descriptions of specimens from Fredericks- 

 burg, Texas, correspond very accurately with those we figure from Fort 

 Washita. 



Figure 6 of plate 3 represents the inferior valve of a large individual 

 from Fort Washita, and figure — of plate — the superior valve of a 

 smaller specimen. 



Exogtra ponderosa, Roemer. 



Exogyra ponderosa, F. Roemer, 1849, Texas, 394. 

 Ostrea ponderosa, D'Orbig., 1850, Prod, de Palseont., II, 256. 

 Exogyra, ponderosa, F. Roemer, Kreid. Texas, 71, taf. ix, fig. 2, a — b. 



Shell thick, ovate, sub-cuneiform ; large valve gibbous, obtusely cari- 

 nated, surface marked with imbricating lamellae ; small valve rather 

 thin, sub-concave, surface uneven, concentrically laminated. Occurs 

 rather abundantly at Fort Washita, generally in a fine state of preserva- 

 tion. Roemer cites this species from New Braunfels, Texas. 



