NEW FOSSIL LAND AND FRESH- WATER MOLLUSKS FROM 

 THE REYNOSA FORMATION OF TEXAS 



By William B. Marshall 



Assistant Curator, Division of Mollusks, United States National Museum 



A lot of fossil mollusks and fossil teeth of mammals submitted for 

 examination by the Roxana Petroleum Corporation of St. Louis, Mo., 

 through John C. Myers of their office at Houston, Tex., was accom- 

 panied by the following data: 



Surface samples of rock containing fossils located in south central De Witt 

 County, Tex., along the Guadalupe River. These samples are thought to be in 

 place, and occur in what is known as the Reynosa Formation of Tertiary Age. 



De Witt County is northeast of central Texas. The Guadalupe 

 River crosses it near its middle, and continuing its southeasterly 

 course finally reaches San Antonio Bay on the Gulf coast. "In 

 1890 Penrose described a deposit of limestone containing many peb- 

 bles and cobbles under the name 'Reynosa limestone,' from the town 

 of Reynosa, Tamaulipas, Mexico. This limestone overlies what was 

 then called the Fayette sand at Reynosa, directly across the Rio 

 Grande from Hidalgo, Tex. Penrose found recent shells embedded 

 in the surface exposures of this formation, and thinking it was Recent 

 included it in his 'post-Tertiary' formations." ^ 



The name "Uvalde formation" proposed by Dumble in 1891 for 

 another part of the same formation is no longer in use. 



The fossil teeth included in the sending were submitted to Dr. J. W. 

 Gidley, of the division of vertebrate paleontology of the United States 

 National Museum, who says they belonged to extinct horses and 

 rhinoceri and indicate that the deposit is probably of the Pliocene 

 series. The fact that the mollusks are all extinct helps to confirm 

 the belief that the formation belongs to the Pliocene. 



The molluscan fossils are in poor condition, but one is sufficiently 

 well preserved to show that it is a land shell, probably of the genus 

 Polygyra. The others are bivalves, most of them internal casts. 

 Some of them retain part of the beak sculpture, the character of 

 which proves beyond doubt that they are pearly fresh-water mussels . 



1 A. C. Trowbridge: Professional Paper U. S. Geological Survey, No. 131-D, p. 98, 1923. 



No. 2798. Proceedings U. S. National Museum, Vol. 76. Art. 1 



41198—29 1 



