6 University of Michigan 



Pisidiuin sp.? "'Two valves and two juveniles, near 

 coiiiprcssiim, but more rounded, less oblique; more 

 like fnllax, but probably distinct" (Sterki). 



11. Staked Plain, Crosbyton, Texas. 



Planorbis Icntus Say var. ? 



12. Double Mountain, Aspermount, Texas. 

 Identified by Clapp. 



Bulimnhis altcrnaUis (Say) var. 



13. Double Mountain Fork of the Brazos, eight miles south- 



east of Aspermount, Texas. 

 Land species identified by Clapp. 

 Polygyra texasiana (Mor.). 

 Zonitoides ininitscnla (Binn.). 

 Zonitoides singleyana Pils. 

 Zonitoides nmnrnus Van. 

 Helicodiscns parallelus (Say). 

 Vallonia costata (Miill.). 

 Pupoides niarginata (Say). 

 Bifidaria cristata P. & V. 

 Bifidaria Jwrdcacella Pils. 

 Bifidaria procera (Gld.). 

 Physa forsJieyi Lea. 

 Planorbis parvus Say. 

 Segmentina obstructa (Mor.) ? Very young. 



14. Red River, Burkeburnett, Texas. 

 Identified by Clapp. 



Zonitoides minnscula (Binn.). 

 Zonitoides singleyana Pils. 

 Zonitoides nummus Van. 

 Vitrea indentata (Say). 

 Pupoides marginata (Say). 



