294 FOSSIL OSTREID^ OF NORTH AMERICA. 



Ostrea congesta (Jonrad. 



(Plate XXXIX, Figs. II, 12, 13.) 



Perhaps no fossil species of oyster is more common and more widely 

 distributed in the Cretaceous strata of western North America than 0. 

 congesta. It is a small shell ; and almost always the lower valve is 

 broadly attached to some foreign body, notably upon the large shells of 

 Inoceramus. 



Ostrea convexa Say. 



(See Gryphma vesicularis, on a following page, with which it is re- 

 garded as identical.) 



Ostrea cortex Conrad. 



(Plate XXXVII, Figs. 3,4.) 



The form to which Conrad gave this name was found by the United 

 States and Mexican Boundary Commission at " Dry Creek, Mexico." 

 It is briefly described on page 157 and figured on Plate IX of Vol. 

 I of the report of that commission. Copies of part of those figures 

 are given on Plate XXXVII ; but they are unsatisfactory, both upon 

 zoological and geological grounds. They will serve, however, to add 

 to the fullness of illustration of the fossil Ostreidse. 



Ostrea crenulata Tuomey. 



Not the 0. crenulata of Lamarck. (See Ostrea tuomeyi Coquand, a 

 Cretaceous species ; not 0. tuomeyi Conrad, a Tertiary species.) 



Ostrea crenulimargo Eoemer. 



(Plate XLHI, Figs. 8, 9.) 



Professor Roemer published this form in Kreidebildungen von Texas, 

 page 76, Plate IX, Figs. 6, a, b. The 0. quadriplicata, afterward pub- 

 lished by Shumard, is almost certainly identical with this species. 

 Lai'ge collections of specimens show intermediate forms connecting 

 those which were described by Professor Eoemer and Dr. Shumard, re- 

 spectively. (See 0. quadriplicata on a following page.) 



Ostrea crenulimarginata Gabb. 



(Plate XL, Fig. 2.) 



This s])ecies is reported from the Cretaceous rocks of Tennessee, and 

 published in the Journal of the Academy of Natural Sciences of Phila- 

 delphia, Vol. IV (n. s.), Plate 68, Pigs. 40, 41. Little is known con- 

 cerning its identity. 



Ostrea cretacea Morton, Owen. 



(See 0. franklini on a following page.) 



Dr. Morton, in his Synopsis of the Organic Eemains of the Creta- 

 ceous Group, page 52, Plate XIX, Fig. 3, published a species under the 



