Occurrence of Ostrea beloiti logan in Cenomanian rocks of Trans-Pecos Texas
— W. A. Cobban and S. C. Hook

The important Upper Cretaceous marine oyster, Ostrea beloiti Logan, has been found at several localities in Trans-Pecos Texas. The species is widely distributed in the Western Interior from Manitoba to New Mexico but heretofore has not been recorded from Texas. However, O. beloiti was found at Cerro de Cristo Rey in New Mexico just west of El Paso, Texas (Strain, 1976, p. 82). This easily recognized oyster usually occurs abundantly in thin beds of coquinid limestone. In Kansas, where the species is especially abundant and conspicuous in the Graneros Shale and Greenhorn Formation, the name Ostrea beloiti Assemblage Zone has been applied (Hattin, 1965, p. 40).

While examining Cenomanian outcrops in Trans-Pecos Texas (fig. 1), we observed O. beloiti in thin beds of calcarenite and coquinid limestone in the lower part of the shaly rocks that overlie the cliff-forming Buda Limestone. These shaly rocks have been referred to as the Eagle Ford Formation in the Eagle Mountains area (Smith, 1940, p. 617; Gillerman, 1953, p. 32), Chispa Summit Formation in the area between the Van Horn Mountains and the Sierra Vieja (Adkins, 1932, p. 426; Twiss, 1959) as well as in the Eagle Mountains (Underwood, 1963, p. 11), Ojinaga Formation in the southern Quitman Mountains (Powell, 1963, p. 309; Jones and Reaser, 1970, p. 11), Boquillas Formation in the Davis Mountains area (Young, 1958, p. 286) and in the El Paso area (Strain, 1968; 1976, p. 82), and Boquillas Limestone in the Davis Mountains area (Brand and Deford, 1962).