6io NORTH AMERICAN INDEX FOSSILS. 



Two to three volutions sharply carinate dorsally, sides sub- 

 angular ; surface pitted. Aperture a little wider than high. 



Common in the Lorraine and Richmond of New York, Canada, 

 Pennsylvania, Ohio, Indiana, Kentucky. 

 26. C. retrorsus Ulrich. (Fig. 815, c y d.) Ordovicic. 



More rapidly enlarging than the preceding ; aperture subquad- 



Fig. 815. a, b, Cyrtolites ornatus (b, enlargement of surface) ; c, d, C. 

 retrorsus ; e-g, C. carinatus. (After Ulrich, Pal. Minn.) 



rangular, keel sharper ; transverse ribs curving backwards on 

 dorsum. 



Black River and Trenton of Kentucky, Tennessee, and Ohio, 

 and Eden of Ohio and Covington, Ky. 



27. C. carinatus Miller. (Fig. 815, e-g.) Ordovicic. 

 Sharply carinate, with latero-dorsal slopes concave ; margin 



notched medially ; sides sharply angulated ; surface without un- 

 dulations, but with lines of growth marked. 



Cincinnatian of Cincinnati region, Wisconsin, Iowa, and probably 

 Minnesota. 



X. Owenella U. and S. 



Thin, subglobose, bellerophontid shells with rounded outer sur- 

 face and gradually enlarging, dorso-ventrally compressed, close- 

 coiled whorls ; open umbilicus, and broad insinuation of the lip 

 without slit band. Cambric. 



28. 0. antiquatus (Whitfield). (Fig. 816.) Cambric. 



b c 



Fig 



. 816. Owenella antiquatus. (After Ulrich and Scof., Pal. Minn.) 



