^BT. 1. EUDISTID SHELLS FROM MEXICO STEPHENSON. 11 



below the Annona tongue of Austin chalk, a mile northwest of 

 White Cliffs, Sevier County, Arkansas. The latter represent an 

 older stage of growth, but they exhibit minor ribbing on the major 

 ribs, which strongly suggests specific identity. 



The species is named in honor of Mr. Ben C. Belt, who was chief 

 geologist of the Mexican Gulf Oil Co. at the time the fossils de- 

 scribed in this paper were collected. 



Locality. — In a gully on the west side of the track of the National 

 Railways of Mexico, 1| kilometers northwest of Chocoy station, 

 about T2f kilometers northwest of Tampico (M. G. O. Acq. No. 141), 

 State of Tamaulipas, Mexico. 



Type.— C^it. No. 32504, U.S.N.M. 



Geologic position.— Lo^^t part of Mendez shale in beds which 

 probably correspond approximately in age to the lower part of the 

 Taylor marl in its type region in central Texas. 



SAUVAGESIA COLORADENSIS. new Bpecies. 



Plates 12-14. 



Discovery aiid occurrence. — The specimen on which this species 

 is based was found in 1919 by Messrs. A. E. Fath and Eugene Steb- 

 inger in reddish shale in the upper part of the Mendez formation, 

 at the series of gullies lf| kilometers northwest of Omaha station, 

 known as El Colorado, where the colony of rudistids described on 

 pages 8 and 9 as Tampsia chocoyensis was obtained. 



Description. — The lower valve is large, elongate, thick shelled, and 

 slightly curved. The specimen was apparently nearly circular in 

 cross section, but the weaker side of the shell has been longitudinally 

 crushed and is now nearly flat. Both the lower and upper ends are 

 incomplete, having suffered fracture and partial destruction. The 

 inner shell layer is wanting and the cavity is filled with red cal- 

 careous clay matrix containing many small foraminifers. 



As preserved the dimensions of the shell are: Length, 155 mm.; 

 diameter of upper end, 90 mm. ; of lower end, 65 mm. ; diameter of 

 upper end of inner cavity. 58 mm. ; of lower end of inner cavity, 

 40 mm. 



The cell structure is only moderately coarse and in cross section 

 the cells are partially arranged in rows roughly parallel to the un- 

 dulations caused by tlie costate surface. The ligamental ridge (pi. 

 12, fig. 2, L) is prominently developed, projecting 4 to 6 mm. into 

 the inner cavity; it is less than a millimeter thick except near its 

 crest, where it flares to a thickness slightly exceeding a millimeter. 



The surface of the shell has been somewhat marred by corrosion, 

 and one side has been flattened by compression. Most of the features 

 are, however, preserved well enough for description. The two si- 



