666 GEOLOGICAL SURVEY OF IOWA. 



PIATE XXIII. FIG. 15 a, b, c. 

 Bellerophon sublcevis : HALL, Transactions of the Albany Institute, Vol. iv, 1856. 



SHELL subglobose, inflated on the last volution. Aperture 

 transverse, arcuate, expanded ; the lip thickened, and much 

 extended at the junction with the volution : umbilicus none ; 

 dorsum carinated by a narrow slightly elevated carina. 



SURFACE ornamented by fine regular striae, which bend 

 abruptly and deeply backwards on the carina, denoting the 

 depth of the emargination of the lip : striae sometimes ir- 

 regular from interrupted growth. 



Length, from -062 to -875 of an inch. 



Fig. 15 a. View of the aperture. 

 Fig. 15 b. Lateral view of the shell. 

 Fig. 15 c. Dorsal view of the same. 



Geological position and localities. In the Warsaw limestone, above Alton, 

 Illinois ; Spergen hill and Bloomington, Indiana. 



Dentalinm primarium ( n. s.). 



PLATE XXIII. FIG. 16. 



SHELL elongate ; the lower half nearly straight and very 

 slightly tapering, gradually curving above and more rapidly 

 diminishing. 



SURFACE marked by fine annulating striae, which at in- 

 tervals become more strongly marked. 



The specimen examined is somewhat exfoliated, and the original surface marking 

 is not fiilly preserved. The species is among the earliest of this genus, several others 

 occurring in the Carboniferous rocks. 



Fig. 16. Lateral view of the specimen, natural size. 



Geological formation and locality. In the Warsaw limestone : Hancock 

 county, Illinois. 



