Pleistocene Snails from San Patricio County, Texas 33 



alternata are known from only the post-Bradyan Bignell loess (Leo- 

 nard, 1952, pp. 176, 182). 



Thus, there is definitive evidence for a Wisconsinan age for the 

 upper unit of the Fordyce sediments, in the geologic ranges of the 

 elements of the fauna (Chart 3), in the absence of any extinct species, 

 and in the change in climatic regimen since the deposition of the upper 

 unit sediments. Indeed, the Fordyce deposits probably represent de- 

 position during post-Bradyan (Late Wisconsinan) times. 



Although there is a similarity between some elements of the fauna 

 of the upper unit of the Fordyce deposits and the upper unit of the 

 post-Eunice Pleistocene Berclair terrace (Conkin and Conkin, 1962), 

 no correlation is hazzarded inasmuch as there are molluscan elements 

 of a cooler and more humid climatic regimen present in the Fordyce 

 Quarry fauna. The more humid environment represented by the For- 

 dyce fauna might be explained by the undoubtedly more vegetated 

 and broader margins of the greater valley and lower altitude of the 

 Nueces River in contrast with the less vegetated and narrower margins 

 of Medio and Blanco creeks at higher altitudes; but the presence in 

 the Fordyce Quarry deposits of characteristically cooler zone snails 

 indicates a difference in climate during deposition of the two deposits, 

 and thus probably a difference in age. 



Chart 3. Previously known range of elements of the Fordyce Quarry fauna (after Pilsbry, 

 1940; Leonard, 1952; and Conkin and Conkin, 1962). 



I "I ' s § -3 I 



(h w oo p O hn 



W >- P=3 



S3 03 



Anguispira alternata 



Gastrocopta armifera 



G. contracta 



G. cristata 



G. tappaniana ; 



Hawaiia minuscula 



Helicina orbiculata tropica 



Polygyra texasiana 



Praticolella berlandieriana 



Pupilla blandi 



Pupoides albilabris 



Retinella indentata 



Retinella indentata paucilirata 



Stenotrema leai aliciae 



Strobilops texasiana 



Succinea grosvenori 





