6 University of Texas Bulletin 



not seem possible to prove that it is the type of Ex. weather- 

 fordensis but it appears at least to be very similar to the 

 specimens described and figured by Cragin ; and it certainly 

 proves that a very near relative of Ex. Boussingaulti lived 

 in the Texas sea at about the epoch of the European species. 

 The specimens from a place four miles west of Montell, 

 also cited by Cragin, may belong to the same species, but 

 they are mainly upper valves, and not very characteristic. 



These last two species seem to grow larger than Ex. Hilli 

 and to a certain degree lead over to Ex. texana and Ex. 

 arietina. The first of these two species is found well de- 

 veloped in the Walnut clays, the base of the Fredericksburg 

 formation. This species has been described and figured by 

 several authors, first by Roemer, 1 then by Conrad, Gabb, 

 Coquand, White, Hill and Vaughan, and by myself. 2 The 

 species is nearly related to Ex. flabellata Goldfuss of the 

 Cenomanian of Europe, but it is in general broader, the ribs 

 are more numerous, and the ridge is nearer to the anterior 

 side ; the European species is generally a little younger than 

 Ex. texana, although this latter passes through quite a num- 

 ber of horizons. In the Walnut clay it is associated with 

 Engonoceras, Schloenbachia group of Sch. Belknapi, and 

 Schloenbachia group of Sch. acutocarinata, and these beds 

 probably represent the Vraconnian or the Albian. It is 

 found also in the Comanche Peak limestone and the Ed- 

 wards limestone; both still belonging to the Vraconnian or 

 Albian. At the Cerro Muleros it occurs throughout the 

 whole Vraconnian. 



It should not be overlooked that the Comanche Peak lime- 

 stone seemingly contains another species of Exogyra, di- 

 rectly derived from the main tribe and exceedingly similar 

 to Ex. Boussingaulti; it is distinguished from Ex. texana by 

 its smooth upper valve, is not very frequent, and I have not 

 seen more than a very few specimens. 



Ex. texana is certainly derived from the tribe of Ex. 

 Boussingaulti represented by Ex. weather fordensis, but the 

 younger species grows much broader, the umbonal ridge 



iRoemer, Kreidebild. v. Texas, 1852, p. 69, pi. 10, fig. la-le. 

 2 B6se, Cerro de Muleros, Bol. Inst. geol. de Mexico, 25. P. 112, 

 pi. 20, fig. 14-16; pi. 21, fig. 1-11; pi. 22, fig. 1-9. 



