32 James E. Conkin, Barbara M. Conkin, William T. Mason, Jr. 



Pilsbry (1940, 1946, and 1948), Baker (1939), Leonard (1950), 

 Franzen and Leonard ( 1947 ) , Forsyth ( 1958 ) , and from observations 

 by the senior author in the field. 



The snail fauna consists of some species that are cosmopolitan in 

 distribution such as Anguispira alternata, Gastrocopta armifera, G. 

 contracta, Hawaiia minuscula, and Succinea grosvenori. Other species 

 are characteristic of a southern climate: Bulimulus alternatus, mariae, 

 Gastrocopta cristata, Helicina orbiculata tropica, Polygyra texasiana, 

 Praticolella berlandieriana, Retinella indentata paucilirata (although 

 it has been reported from Indiana), and Strobilops texasiana. It should 

 be noted that the bulk of the snails as presented in chart 2 are domi- 

 nantly of a southern climatic regimen. Freshwater snails are cosmo- 

 politan and indicate ponded waters of creeks and rivers. 



Many of the species herein reported are characteristically found 

 along watercourses, thus being restricted to humid stations even in 

 semi-arid regions. However, some species recovered from the samples 

 definitely indicate a cool and humid climate; these are: Gastrocopta 

 tappaniana, Pnpilla blandi, and to a lesser extent, Retinella indentata 

 (characteristically a temperate to north-temperate species). 



The sedge genus Scleria? is indicative of locally, but not region- 

 ally, moist environment. 



The evidence presented herein, based upon considerations of the 

 geographic distribution and ecological requirements of the species of 

 snails, indicates that climatic conditions were different during the time 

 of deposition of the sediments of the upper unit at the San Patricio 

 site than during the Recent in this area. The subsequent disappear- 

 ance of Pupilla blandi and Gastrocopta tappaniana and diminuation 

 of other forms in the Recent is consistent with the change to a warmer 

 and drier climate in south Texas after deposition of the upper unit of 

 the Fordyce deposits. 



Age of the Deposits 



Although some species of snails in the upper unit of the Fordyce 

 deposits are known in the fossil record as far back as the Aftonian, 

 and one species, Pupoides albilabris, is recorded from the Pliocene, the 

 bulk of the fauna is not known stratigraphically below the Yarmouth- 

 ian. Three species, Helicina orbiculata tropica, Praticolella berlandier- 

 iana, and Stenotrema leai aliciae, are not known prior to the Wiscon- 

 sinan; all three of these species were reported from the post-Eunice 

 Pleistocene by Conkin and Conkin (1962, p. 348). Pupilla blandi is 

 known from the pre-Bradyan Wisconsinan. In the well known Pleisto- 

 cene sequence of Kansas, Stenotretna leai aliciae and Anguispira 



