TERTIARY PERIOD. 209 



Class GASTEROPODA. 



Subclass PULMONIFERA. 

 Order PULMONATA. 



Suborder BASOMMATOPHORA. 



Family LIM^MIDM. 



Genus PLANORBIS Guettard, 1756. 



Planorbis Utahensis Meek. 



Plate XXI, fig. 8 a. 



Planorhis Utahensis Meek, 1860, Proc. Acail. Nat. Sci. Phila., 314. 



Shell moderately large, discoidal, compressed, slightly convex above ; 

 test thin ; the first two or three volutions often depressed a little below the 

 general surface of the outer ones, making the top slightly concave at center ; 

 umbilicus broad, not very deep, showing all the inner volutions plainly; 

 volutions from four to five and a half, rather slender, wider than high, sub- 

 elliptical in transverse section, convexity of the tipper side slightly less than 

 that of the lower side ; u^jper side of the outer volution slightl}^ sloping 

 outward and downward to the periphery, which is somewhat naiTowly 

 rounded; suture distinct, but not very deep above, deeper and more distinct 

 below; a small part of each volution concealed by the next succeeding 

 one ; aperture suboval, slightly expanded laterally. 



Surface marked by small oblique lines and occasional small wrinkles 

 of growth. These lines extend obliquely outward and backward, the margin 

 of the aperture also having the same direction. 



Greatest breadth of the largest specimen in the collection, twenty-four 

 milhmeters. Mr. Meek's type-specimens were obtained from Tertiary strata, 

 which he was disposed to regard as Eocene, in the valley of Ham's Fork, 

 latitude, 41° 40' north; longitude, 110° 10' west. 



Position and locality. — Sti-ata of Tertiary age; east slope of Pine Mount- 

 ain and at Castle Valley, Utah. 



14 P 



