436 CRETACEOUS PALEONTOLOGY. 



1884. Ostrea congesta White, 4th Ann. Rep. U. S. G. $., p. 294, 



pi. 39, figs. 11-13. 

 1893. Ostrea congesta Stant, Bull. U. S. G. S., No. 106, p. 55, 



pi. 2, figs. 2-4. 



Description. Shell small, the individuals often crowded closely 

 together in considerable numbers, so as to assume quite irregular 

 forms. Surface of attachment of the lower valve large, beyond 

 which the margin of the shell is abruptly deflected upward at 

 right angles to the attached portion ; upper valve flat or a little 

 concave, having the form of the attached portion of the lower 

 valve. 



The dimensions of a specimen referred to the species are: 

 length, 12.5 mm.; width, 15 mm. 



Remarks. A number of individuals of a small oyster have 

 been observed in the Cliffwood clays which seem to belong to this 

 species. The species may be recognized chiefly by the propor- 

 tionately large area of attachment, with the abruptly deflected 

 margins of the lower valve. 



Formation and locality. Cliffwood clay, Cliffwood Point 



(105). 



Geographic distribution. New Jersey, Kansas, Nebraska, 

 South Dakota, Colorado, New Mexico. 



Ostrea denticulifera Conrad. 

 Plate XLIIL, Figs. 1-2. 



1858. Ostrea denticulifera Con., Jour. Acad. Nat. Sci. Phil., 

 2nd ser., vol. 3, p. 330, pi. 34, figs, i and 8. 



1861. Ostrea denticulifera Gabb, Synop. Moll. Cret. Form., p. 

 208 (152). 



1864. Ostrea denticulifera Meek, Check List Inv. Foss. N. A., 

 Cret. and Jur., p. 6. 



1868. Ostrea denticulifera Con., Cook's Geol. N. J., p. 724. 



1869. Ostrea denticulifera Coquand, Monog. Gen. Ostrea Terr. 



Cret., p. 50, pi. 17, figs. 8-9. 



1884. Ostrea denticulifera White, 4th Ann. Rep. U. S. G. S., 

 p. 295. 



