PLEISTOCENE SNAILS FROM SAN PATRICIO COUNTY, TEXAS 



JAMES E. CONKIN, BARBARA M. CONKIN, AND WILLIAM T. MASON, JR. 

 University of Louisville 



Abstract 



Pleistocene deposits in the Fordyce Quarry at San Patricio, San 

 Patricio County, Texas are divided into two units: a fossiliferous upper 

 unit consisting of silt with caliche and minor amounts of sand, and a 

 lower unit of gravel and sand, barren of fossils except fragments of 

 reworked extinct Pleistocene vertebrates and reworked Devonian, 

 Cretaceous, and Tertiary fossils. 



A snail fauna is identified from the silt and sand of the upper unit 

 consisting of 17 genera including 18 species of land snails and three 

 species of freshwater snails. Sixteen species of land snails and two 

 species of freshwater snails are reported for the first time from the 

 Pleistocene of San Patricio County. Bulimulus alternates inariae, Eu- 

 conulus cher sinus trochulus, Helisoma tenue sinuosum, and Armigerus 

 obstriictus are reported as fossils for the first time. Gastrocopta con- 

 tracta is reported as a fossil from Texas for the first time. Gastrocopta 

 armifera, G. tappaniana, and Pupoides albilabris are reported as fossils 

 from south Texas for the first time. 



Some species, such as Gastrocopta tappaniana and Pupilla blandi, 

 in the Fordyce Quarry fauna are characteristic of cool and humid 

 climates, or certainly of temperate zones to the north. Pupilla blandi 

 is not known in the Recent of Texas, while Gastrocopta armifera and 

 G. tappaniana are not known in the Recent of south Texas. Thus a 

 cool and somewhat more humid climatic regimen is indicated for south 

 Texas during the deposition of the sediments of the upper unit in the 

 Fordyce Quarry. The presence of the sedge genus, Scleria?, is an in- 

 dicator of locally moist environmental conditions, but not of the 

 regional climatic regimen. 



Evidence derived from the geographic distribution and ecological 

 requirements of many species, the absence of extinct species of snails 

 and vertebrates, coupled with evidence based on the geologic range 

 of the fossil snails indicate that the sediments of the upper unit of the 

 Fordyce Quarry were deposited during Late Wisconsinan times. Some 

 of the species have long stratigraphic ranges; nevertheless, the overall 

 aspects of the mollusks is Wisconsinan. Pupilla blandi is known from 

 the pre-Bradyan (Early Wisconsinan), but Anguispira alternata and 

 Stenotrema leai aliciae are known from only the Bignell loess of Late 

 Wisconsinan ( Mankatoan, post-Bradyan ) age in the classic Pleistocene 

 section of Kansas. 



