PVRGULOPSIS SCALARIFORMIS. I7I 



Zonites arbor ens. Say. LimncBa ca-pcrata., Say. 



Zonites indcntatus. Say. Limncea /niniilis, Say. 



Alesodon inuUilineata, Say. Limncea desidiosa, Say. 



Mesodon clausa. Say. Physa gyrina, Sa}'. 



Mesodon ■profunda, S ay. Planorbis trivolvis, Say. 



Pupa contractu, Say. Planorbis parvus. Say. 



Piipa pcntodon. Say. Scgmentina arnijgera, S^y. 



Succinca obliqua. Say. Ancylus rhularis. Say. 

 Succinca avara. Say. 



A total of thirty-eight species. 



All of these species are now found living either in the im- 

 mediate vicinity of of this deposit, or in the Mississippi and its 

 tributaries not far away, the Pyrgidopsis being, so far as we 

 know, the only extinct species which occurs in the deposit. 



The fact that this species is a fossil led the writer to further 

 compare it with Pyrgula scalariformis, which was described 

 by Mr. John Wolf in 1869 ^ as a "post-pliocene fossil." 



The result of this comparison establishes the identity of P. 

 scalar if orniis and P. mississippiensis beyond all doubt. 



Mr. Wolf's description 2 is as follows : 



"Shell turreted, slender; whorls six, chalky-white; suture 

 deeply impressed; carinate its entire length on the lower edge 

 of the whorls; mouth small, ovate, but slightly connected with 

 the last whorl. Length one-half inch. Post-pliocene; abund- 

 ant on the Tazewell shore of the Illinois river." 



For comparison the description of P. mississippiensis is 

 added. 2 



"Shell minute, pupiform, elevated, imperforate; whorls 

 5/^-6, flattened, with a well-marked carina on lower third, 

 which becomes central on periphery of last whorl, body-whorl 

 equal to one-half entire length of shell and bluntly angulated 



1 Am. Journal of Conchology^ Vol. V, p. 19S. 



2 Copied in Proc. Dav. Acad, of Nat. Science^ Vol. V, p. 14, from the Am. 

 Jour, of Co7ichoIogy, Vol. V, p. 19S. 



3 Proc. Dav. Acad. Xaf. Science, Vol. V, p. 13; 1SS6. 



