WHITE] CRETACEOUS. 305 



Exogyra fimhriata Conrad, 



This proposed species is really unworthy of notice, because its original 

 description was based upon only a single upper valve, which is probably 

 that of a small example of Exogyra ponderosa. Conrad published it in 

 the Report of the United States and Mexican Boundary Survey, Vol. I, 

 page 154, Plate VII, Figs. 2, «., h. Adding still further to unnecessary 

 synonymy, the name is, by tyi)ographical error, given as E.foliacea on 

 Plate 7, Vol. I of the United States and Mexican Boundary Survey. 

 Furthermore, Coquand, in his Monogra])hie du Geni-e Ostrea, page GO, 

 l)roposed to change Conrad's supposititious name to 0. nabfimbriata. 



Exogyra forniculata White. 



(Plate LII, Figs. 1,2.) 



The gradation of the genus Grypliwa, which has before been referred to, is 

 exemplified by this species, which might with equal propriety be referred 

 to either genus. The principal distinguishing characteristic of Exogyra 

 I have taken to be the lateral deflection and greater or less curvatui'e 

 of the beak of the lower valve. The full development of this feature is 

 shown in such forms as E. costata and E. laiviuscula, and the minimum, 

 in the species heading this paragraph. So fiir as I am aware Exogyra 

 forniculata has been found only in Texas and the adjacent parts of 

 Mexico. It has often been confounded with the variety of Gryphaa 

 pitcheri to which Conrad gave the name G.navia. It was originally pub- 

 lished as a distinct species in the Proceedings of the National Museum 

 Vol. II, page 293, Plate IV, Figs. 3, 4 ; and subsequently in the Annual 

 Eeport of the United States Geological Survey of the Territories, page 

 13, Plate 14, Figs. 2, a, b. 



Exogyra fragosa Conrad. 



This form is perhaps only a variety of E. ponderosa, but it was pub- 

 lished as a distinct species by Conrad in the Report of the United States 

 and Mexican Boundary Survey, Vol. I, Plate VIII, Figs. 2, a, b. It 

 was obtained from Cretaceous strata of Texas. 



Exogyra interrupta Conrad. 



Mr. Conrad published a form under this name from the Cretoceous 

 strata of Mississippi in the Journal of the Academy of Natural Sciences 

 of Philadelphia, Vol. Ill (n. s.), page 330, Plate 34, Fig. 15. The figure 

 is very unsatisfactory, and ajjparently )epr(>sents a young and small 

 example of the lower valve of ^ species like E. icinclieUi. 



Exogyra Icevinscula Ecemer. 



(Plate LII, Figs. 3, 4, 5.) 



Professor Eoemer published this species from the Cretaceous strata of 

 Texas in his Kreidebilduug von Texas, page 70, Plate IX, Figs. 3, a, b, 

 3 INT 20 



