PLATE XXIV. 



PAGE. 



CTBNACANTHUS GBACILLIMUS, N. and W 238 



Fig. 1 o. Side view of a nearly entire dorsal spine. St. Louis limestone; Shumard 

 collection of Washington University, St. Louis, Missouri. 



OBACANTHUS VETUSTUS, Leidy 256 



Fig. 2 a. View of right side of spine; 2 b, c, do., transverse sections toward tip and 

 near middle, showing thickness of the walls inclosing pulp cavity; 2 d, 

 do., enlargement of tubercle. St. Louis limestone. St. Louis, Missouri. 

 Museum Washington University. 



ACONDYLACANTHUS? MuDGiANUS, St. J. and W 244 



Fig. 3 a. View of fragment, showing a strip of the right side near the postero-lateral 

 border with the longitudinal costae, and part of the opposite side em- 

 bedded in the limestone matrix, with the pulp cavity exposed to view; 

 3 b, do., transverse section of spine. Upper Coal Measures; Rock creek, 

 near Manhattan, Kansas. Mr. St. John. 



GYBACANTHUS? COBDATUS, St. J. and W 2S1 



Fig. 4 a. View of right side of spine, portion of inferior wall broken away exposing 

 to view inner surface of the opposite wall; 4 b, do., transverse section 

 near middle, the anterior border uppermost. St. Louis; Alton, Illinois. 

 Mr. Butters. 



DBEPANACANTHUS BEVEBSUS, St. J. and W 253 



Fig. 5 a. View of right side of spine; 5 b, c, do., transverse sections toward tip and 

 near dorsal line. St. Louis; Alton, Illinois. Mr. Butters. 



PHTSONEMUS FALCATUS. St. J. and W 252 



Fig. 6 a. View of spine from the right side, base^partially restored; 6 b, do., trans- 

 verse section toward tip. St. Louis; St. Louis, Missouri. Washington 

 University. 



