304 FOSSIL OSTEEID^ OF NORTH AMERICA. 



on page 156 of Binney's edition of Say's writings and Mrs. Say's excel- 

 lent figures of it on Plate 7 of that volume. 



Conrad published this species under the name of Exogyra caprhia in 

 the Journal of the Academy of Natural Sciences of Philadelphia, Vol. 

 II (n. s.), page 273, Plate XXIV, Figs. 3, 4. Koemer's name must 

 remain, however, because it was previously published, unless the name 

 Exogyra laxa Say shall be used. 



Exogyra aquila Goldfuss. 



(Plate LIII, Figs. 1, 2.) 



The specimens which are here recognized as belonging to the Exogyra 

 aquila of Goldfuss were sent to the Smithsonian Institution some years 

 ago by Mr. D. A. Walker, from Bell County, Texas. CTpou comparing 

 them with the figures given by Goldfuss in his Petrefacta Germanise, 

 page 36, Plate 87, Fig. 3, no features appear to me npon which a specific 

 difference can be based. I am not aware that this species has before 

 been recognized in American strata, but various authors have reported 

 it from different parts of Europe and from both Northern and Southern 

 Africa. 



Exogyra columbella Meek. 



(Plate LV, Figs. 5, 6.) 



This small species of Exogyra has hitherto been found only in Southern 

 Utah and the adjacent parts of New Mexico, where it is sometimes found 

 associated with E. Imviuscula Ecemer, which species it resembles in size. 

 Itwas published by myself in the reports of United States Explorations 

 and Surveys west of the 100th Meridian, Vol. IV, page 174, Plate XVII, 

 Figs. 3, «, h, c, d. I there regarded it as a small variety of E. costata, 

 and gave it the variety name of fluminis. In the same year Mr. Meek 

 published this form under the name of E. cohimbella, in the Eeport of 

 Macomb's Exploration, page 124, Plate I, Figs. 3, a, b, c, d. 



Exogyra costata Say. 



(Plate LVI, Figs. 1, 2; Plate LVII, Figs. 1, 2.) 



This is one of the most common and characteristic as it is one of the 

 largest species of JE/j;o<72/ra that are found in the Cretaceous rocks of the 

 United States. It is especially characteristic of certain strata in the 

 Atlantic and Gulf States, and also in Mexico. It is usually quite con- 

 stant in its form and in the costate character of its surface, but in the 

 latter respect it is sometimes variable. Indeed, some authors regard 

 Exogyra ponderosa Eoemer as only a variety of E. costata, differing only 

 in the obsolescence of its costfe. This feature is so constantly present 

 in the one form and absent in the other that I prefer to regard them as 

 representing distinct species. 



