190 SYSTEMATIC PALEONTOLOGY 



Pecten sp. 

 Plate XLiy, Pigs. 9, 9a. 



Pecten sp. Clark, 1895, Johns Hopkins Univ. Circ, vol. sv, p. 5. 



Pecten sp. Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 86, pi. xxxiv, fig. 4. 



Description. — " Shell small, orbicular; surface with about twenty 

 broad, flat costae, dividing in most cases in passing downward, so that 

 over thirty appear at the margin; umbones compressed; ears unequal." 

 Clark, 1896. 



This differs from P. johnsoni only in having the ribs increase by 

 bifurcation instead of intercolation, and in having the ribs broader than 

 the interspaces. As the figured specimen is the only one that has been 

 found and is very immature it is best not to give it a name. Perhaps it 

 is an aberrant or immature form of P. johnsoni, or of P. wahtuhieanus 

 Ball. 



Width, 10 mm.; height, 11 mm. 



Occurrence. — Aqijia PoEMATioisr. Potomac Creek. 



Collection. — Maryland Geological Survey. 



Family OSTREIDAE. 



Genus OSTREA Linne. 

 OSTEEA COMPEESSIEOSTfiA Say. 



Plates XLV, XLVI, XLVII. 



Ostrea compressirostra Say, 1834, Jour. Acad. Nat. Sci. Phila., vol. iv, p. 133, pi. viii, 



figs. 3a, 3& [Reprint Bull. Amer. Pal. No. 5, p. 38, pi. viii, figs. 3a, 36.] 

 Ostrea compressirosira Morton, 1834, Syn. Org. Rem. Cretaceous Group, App., p. 3. 

 Ostrea sinuosa Rogers, 1837, Trans. Amer. Pbilos. Soc, vol. v, p. 340; vol. vi, 



pi. xxvii, fig. 1. 

 Ostrea compressirostra H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 103. 

 Ostrea hellovacina Conrad, 1843, Proc. Nat. Inst., Bull, ii, p. 173 (not of Lamarck). 

 Ostrea sinuosa H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 103. 

 Ostrea compressirostra Conrad, 1865, Amer. Jour. Conch., vol. i, p. 15. 

 Ostrea sinuosa Conrad, 1865, Amer. Jour. Conch., vol. i, p. 15. 

 Ostrea compressirostra Conrad, 1866, Smith. Misc. Coll. (200), p. 3. 

 Ostrea compressirostra Heilprin, 1883, White's Fossil Ostreidae ; Fourth Ann. Rept. 



U. S. Geol. Survey, p. 309, pi. Ixv, figs. 1, 2. 

 Ostrea compressirostra Heilprin, 1884, Contrib. Tert. Geol. and Pal., p. 85. 

 Ostrea sinuosa Rogers, 1884, Geology of the Virginias, p. 668, pi. ii, fig. 1. 

 Ostrea compressirostra de Gregorio, 1890, Ann. Geol. et Pal., t. ii, p. 177, pi. xx, 



figs. 1, 8. 



