170 Natural History Bulletin. 



contains great numbers of fresh-water mollusks, the distinc- 

 tively fluviatile forms such as Lamellibranchs, i^S-phcerium^ 

 Pisidmin, and occasionally Uiiio), and the operculate Gastero- 

 poda^ ( Campeloma, Pleurocera^ Aimiicola^ Pyrgulofsis, Soma- 

 iogyrtts, etc.,) forming by far the greater pro.portion. 



Some parts of this stratum are almost entirely made up of 

 bleached shells. 



In this stratum were found numerous specimens of the 

 species under discussion, and though careful search was made 

 none were found in places other than those to which the 

 shells could easily be carried by the waters of Rock River 

 from this deposit. 



The folio win a- list of the shells found associated with the 

 Pyrgtilopsis may be of interest: 



LAMELLIBRANCHIATA. 



SfhcBrium sh'iatinuvi, Lam. Pisidiuni abdihmi, Hald. 

 Sphcermm sulcatum, Lam. Uitio fragments. 



GASTEROPODA. 



Prosobranchiata. 



,Plcuroccra subularc. Lea. Pomatio-psis lap>idaria. Say. 



BithyncUa obtusa, Lea. Valvata tricarmata^ Say. 



Amnicola limosa. Say. Valvata bica?'inata. Lea. 



Amnicola cincinnatensis, Anth. Vivipara intertexta^ Say. 



Amnicola say ana, (?) Anth. Camp)eloma subsolidum, Anth. 



Somatogyrus subglobosus, Say. Camfcloma coarctattnn, Lea. 

 Somatogyrus integer. Say. 



Pulmonata. 



Zonites radiatulus. Alder. Succinea ovalis, Gld. 



Zonites niinusculus, Binn. Limncea rejiexa, Say. 



