POSTGLACIAL BIOTA OF THE GREAT LAKES REGION 125 



inadequate to account for the present shell stratum. The deposits are evidently 

 the same as those described above by Tiffany. Thirteen fluviatile and four 

 land mollusks are listed by Pratt. 



Fusconaja undata { = trigonus) Obovaria ellipsis 



Crenodonta plicata Nephronajas ligamentina 



Quadrula pustidosa Vivipara subpurpurea 



" metanevra Campeloma subsolidum 



Rotundaria tuberctdata ( = verrucosus) Polygyra profunda 

 Plethobasus aesopus " thyroides 



Elliptio crasidens " midtilineata 



" gibbosus Pyramidula alteranta 

 Obliquaria reflexa {—cornidus) 



Limnaea (Galba) tazewelliana and Pyrgulopsis scalariformis, described by 

 Wolf 21 from post-Pliocene deposits on the Tazewell side of the Illinois River, 

 are probably referable to the same age as the Rock Island fauna. No fossil 

 species other than the Lymnaea (now known as Galba parva) and the Pyrgulop- 

 sis have been recorded from this locality, altho they are doubtless to be found 

 in the same deposits. Leverett 22 reports "molluscan shells in sand at 6-10 

 feet" from section 3-4, T.33, R.5E, LaSalle County, but the nature of the 

 shells is not stated. 



Near Mahomet, Sangamon County, on the Sangamon River, fresh-water 

 mollusks have been collected by Dr. T. E. Savage, of the University of Illinois, 

 in a sand stratum about four feet below the surface. The species, 8 in number, 

 are mostly fluviatile, and are listed below: 



.Vnio, fragments Amnicola limosa porata 



Sphaerium solidulum Pleurocera elevalum 



Pisidium compressum Planorbis antrosus 



Campeloma integrum (young) Pyramidula solitaria 

 Valvata tricarinata 



About three-quarters of a mile below Mahomet, on the north bank of the 

 Sangamon River, a sand stratum occurs in the flood plain of the river, about 

 8-12 inches below the surface of the river and five feet above the level of the 

 water (in July). The deposit is several hundred feet in extent and is evidently 

 somewhat younger than the deposit examined by Savage. The species col- 

 lected from this stratum are noted below: 



SpJtaerium sulcatum . Valvata, bicarinata 



" stamineum Amnicola limosa 



solidulum Pleurocera elevatum 



Pisidium virginicum Planorbis antrosus 



compressum illinoisesnse " campanulatus 



Campeloma integrum Pyramidula alternata 



21 Amer. Journ. Conch., V, p. 198. 



22 Illinois Glacial Lobe, p. 640. 



