389 The Oligocene of the Southern United States 79 



Unio cretacollis sp. nov., PI. 29, fi{<. 4 



Shell of medium size, broadl}- elliptical, slightly winged at 

 the dorsal margin. Posterior area marked off from the anterior 

 by a rounded plication which passes from the beak to the posterior 

 extremity. Beaks low, placed at the anterior sixth of the shell. 

 Length of shell, 60 mm., height, 45 mm. 



ANODONTA Lamarck 

 Anodonta Cornelliana sp. nov., PI. 29, fig. 3, 5, 6, 7 



Shell elongate -oval, apparently thin and light. Posterior 

 extremity prolonged and sharply pointed, anterior rounded. 

 Posterior area defined by a sharp carina, passing from the beak 

 to the posterior extremity. Lines of growth delicately impressed. 

 Beak rather prominent, placed at the anterior fifth of the shell. 

 Beak sculpture concentric. Length of shell, 75 mm., height, 

 30 mm. 



The Frio clays. The Frio clays have been traced by Mr. 

 Veatch in the southwestern part of Louisiana. They overlie the, 

 Grand Gulf beds and are a continuation of the Texas formation 

 which thins out and disappears in Louisiana. 



Texas. 



The Grand Gulf sandstones. The Grand Gulf sandstones 

 continue from Louisiana into Texas, and pass through that state 

 in a westerly and southwesterly direcflion, forming a belt of some 

 12 miles in average width. 



Dr. Hilgard,* in 1871, suggested the continuation of the 

 sandstone series from the Sabine to the Rio Grande Rivers. In 

 1880, this was confirmed by the observations of Mr. R. H. Lough- 

 ridge, f who traced the sandstone from Trinity River to the Rio 

 Grande by a(5lual outcrops. 



Mr. R. Penrose, t in 1889, named the formation the 'Fayette 

 beds,' but regarded them as equivalent to the Grand Gulf .series. 



* Miss, embayment, Proc.Amcr. Assoc. Adv. Sci.,\o\. 20, map opp. p.222. 



t Census Report, vol. 5, 1880, p. 679. 



X Rep. Geol. Gulf Tcrtiaries of Texas, p. 47. 



