10 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 61, 



probably within 200 feet (60 meters) of the top of the formation. In 

 other words, the stratigraphic position of the type is not very different 

 from that of the fragments here described, a fact which lends strength 

 to the assumption that the fragments represent the same species as 

 the type. 



The species is closely related to Sauvagesia helti^ but differs from 

 that species in the absence of minor ribbing on the major ribs. 



Localities. — State of Tamaulipas, District del Sur: Las Flores 

 hacienda (Manuel ranch), in an arroyo 3^ kilometers west by north 

 of Manuel station (M. G. O. Acq. No. 135), in an arroyo 6 kilometers 

 west by south of Manuel station (M. G. O. Acq. No. 138), and in an 

 arroyo about 1\ kilometers west by south of Manuel station (M. G. O. 

 Acq. No. 139) ; Chocoy hacienda or ranch, in an arroyo about 3 kilo- 

 meters north-northwest of Chocoy station (M. G. O. Acq. No. 143). 



Type. — The type specimen is in the United States National 

 Museum at Washington as Cat. No. 32482. 



Geologic position. — The specimens from Chocoy and Manuel 

 haciendas occur in the upper part of the San Felipe formation, which 

 is correlated approximately with the upper part of the typical Austin 

 chalk in the vicinity of Austin, Texas. 



SAUVAGESIA BELTI, new species. 



Plate 11. 



Occurrence.— Tlh\^ species is represented by one incomplete indi- 

 vidual found by the writer near the railroad about 1^ kilometers 

 northw^est of Chocoy station. The specimen is a portion of the lower 

 valve on the side opposite to that which bears the siphonal areas and 

 includes less than half the circumference of the shell. The length 

 of this fragment as preserved is 87 mm., and the shell flares from a 

 width of about 20 mm. at the base to a width of 75 mm. on corre- 

 sponding costae at the top. 



The surface of the fragment is ornamented with 8 major costae 

 which increase in size away from the base and which differ consider- 

 ably in size; each of the major costae is ornamented with numerous 

 minor irregular costae which differ somewhat in size from the base 

 upward ; the effect of complexity is further increased by a tendency 

 of the growth layers to form imbricating lamellae. 



The inner shell layer is not preserved. The outer shell layer is 

 thick and exhibits the rather coarse cell structure which character- 

 izes the genus; the ligamental ridge (L) is strongly developed though 

 imperfectly preserved along the entire length of the shell ; the inner 

 surface of the shell is finely cancellated due to the crossing of the 

 fine growth lines and a series of fine longitudinal lines. 



The species is closely related to fragments of Sauvagesia found 

 in the United States in the upper part of the Brownstown marl, just 



