12 University of Texas Bulletin 



venile stages of Ex. ferox have been found and described. 

 The species was found in the so-called lower Cross Timber 

 (Woodbine) sands, which correspond in age probably to the 

 Buda limestone; at least, they also belong in their lower 

 part to the upper Cenomanian. 



It is difficult to say to what group belongs the form cited 

 by Cragin 1 as Ex. columbella Meek. It certainly has noth- 

 ing to do with the type of that species. The specimen which 

 came from the lower Cross Timber sands of Timber Creek, 

 two miles below the Dallas-Lewisville Road, Denton County, 

 is so much corroded that the surface appears nearly smooth, 

 but on close inspection one can easily see that it had been 

 covered by thick, rounded, rather strong ribs. It might be 

 a very young individual belonging to the group of Ex. 

 Clarki. 



From the next higher beds, the Eagle Ford shales, which 

 correspond to the Turonian, very few fossils have been de- 

 scribed in Texas, and among these only one Exogyra is 

 cited under the name of Ex. columbella Meek. This is a 

 rather small form with thin shell and covered by small, 

 quite regular, radial ribs, which bifurcate at the umbonal 

 ridge. It seems to be very possible that this species is a 

 branch of the Ex. Clarki group, if it is not directly derived 

 from Ex. arietina through the so-called Ex. columbella 

 Cragin. This may only be decided when larger collections 

 in the Eagle Ford shales or the upper part of the Wood- 

 bine sands shall have been made. In Colorado a large 

 species, Ex. suborbiculata Lam., occurs, which as Stanton 

 justly remarks, is intimately related to the European group 

 of Ex. columba, but this larger form has not yet been found 

 in Texas. 



Also in the next higher formation, the Austin Chalk, very 

 few Exogyras are known, although they can be found in 

 great numbers in it. The Austin Chalk corresponds in its 

 lower part to the Emscherian, in its middle to the lower 

 Santonian, and in its upper part to the middle Santonian. 

 I have not seen any Exogyra in the lower part, but it is 



Cragin, loc. cit., p. 184. 



