Fic. 1 
14,1» 
Figs. 2,3. 
28, Qb. 
Fic. 4 
4a 
4b 
282 
PLATE XXWiA: 
CTENACANTHUS CYLINDRICUS, Newb. (p. 202). 
. Spine, natural size; view of anterior face. 
. Sections. - 
Keokuk group, Kentucky. 
CTENACANTHUS CLARKH, Newb. (p. 168). 
Spine, natural size; views of opposite sides of same specimen. 
Sections. 
Cleveland shale, Berea, Ohio. 
CTENACANTHUS WRIGHTI, Newb. (p. 66). 
. Spine, natural size; side view. 
. Section near summit. 
. Ornamentation enlarged. 
Hamilton group, Yates County, N. Y. 
