OF CONCHOLOGY. 315 



3. Description of a nno Fresh- Water ayid a Land Shell of the 

 Oregon Tertiary. 



HELIX, Lin. 

 Subgenus Zonitbs, Montf. 

 n. MARGINICOLA, Conrad. PL 13, fig. 9. 



Depressed ; spire scarcely raised above the margin of the last 

 volution ; whorls 6, convex-depressed ; shoulder of last whorl 

 subangular ; umbilicus small ; aperture obliquely subquadrate. 



PLANORBIS. 

 Subgenus Spirorbis ? Swains, 



P. LUiSTATUS, Conrad. Pj. 13, fig. 8. 



Spire profoundly depr essed with a subangular margin ; um- 

 bilicus with a rounded margin, profound, and exhibiting 6 volu- 

 tions ; aperture narrow, lunate. 



Locality. Bridge Creek, Oregon. 



Dr. Leidy informs me that these two shells were found by 

 Rev. Thomas Condon, of Dallas City, Oregon. They were in 

 the same rock which contains the remains of Oreodon superbus, 

 Leidy, Lophiodon and Rliinoceros. 



