664 GEOLOGICAL SURVEY OF IOWA. 



SURFACE marked by fine regular concentric lines parallel 

 to the border of the shell. 



Length, -11 to '13, width -08 to -10 of an inch. 



Fig. 10 a, b. Dorsal view, and view of the right valve. 



Fig. 10 c. The same enlarged. 



Fig. 10 d. Enlargement of the concentric striae. 



Geological position and locality. In limestone of the age of the Warsaw 

 limestone : Spergen hill, Indiana. 



Cypricardella subelliptica. 



PLATE XXIII. FIG. 11 & 12. 

 Cypricardella subelliptica : HALL, Transactions of the Albany Institute, Vol. iv, 1856. 



SHELL subelliptical, obliquely truncated at the posterior 

 end. Beaks minute at the apex, rising little above the hinge : 

 umbones subgibbous, with an undefined elevation extending 

 obliquely towards the posterior basal margin ; anterior end 

 narrower than the posterior, rounded at the extremity. Car- 

 dinal margin forming an angle with the beak of 25 : base 

 forming a regular elliptical curve. 



SURFACE marked by regular fine concentric elevated lines, 

 which are equal to the spaces between. 



Length, -19 to -32, width -14 to -24 of an inch. 



Fig. 11. View of the right valve. 



Fig. 12. Interior of the same, showing the character of the hinge-line. 



Geological position and locality. In limestone of the age of the Warsaw 

 limestone : Spergen hill, Indiana. 



Pleurotomaria wortheni. 



PLATE XXIII. FIG. 13 a, b, c, d. 

 Pleurotomaria wortheni : HALL, Transactions of the Albany Institute, Vol. iv, 1856. 



SHELL depressed subglobose : spire but little elevated, 

 oblique from the great expansion of the last volution. Vo- 

 lutions about three, somewhat flattened above, rapidly ex- 

 panding so that the last volution makes nearly the whole 

 bulk of the shell, obtusely angulate on the periphery : upper 

 margin of the volutions marked by a row of strong nodes, 

 which extend about one-third across. 



