PLATE XXI. 



PAGH. 



Fig. 1-3. Batacanthus btellatus (UT. and TV. sp.) 470 



1 a. Side "view of an imperfect and worn spine, showing large tubercles in the upper por- 

 tion of the posterior border, the spinose tubercles of the middle and lower anterior 

 side, and outline of pnJp cavity ; 1 b, sketch of upper portion of the posterior side, 

 showing ainangeraent of tubercles; 1 c, transverse section; 1 d. enlargement of 

 one of the large posterior tubercles, seen from above and profile outline; 1 e, 

 enlarged sketch of tubercles of tbe lateral faces. The original specimen figured in 

 Vol. II, PI. 12, fig. 7. Geode bed of the Keokuk j Warsaw, Illinois. 

 3 a. Side view of fragment of tbe middle portion of a similar spine, the tubercnlation of 

 the lateral surfaces nearly obsolete from abrasion, hut showing the bases of the 

 anterior tubercles; 2 I, sketch of anterior face, showing disposition of tubercles; 

 2 c, transverse section. Upper tish-bed Keokuk limestone; Hamilton, Illinois. 



3 a. Side view of a larger specimen, preserving 1he anterior tubercles entire; 3 b, c, d, 



enlargements of tubercles from middle region near base, from the upper portion 

 near the posterior side, and one of the large anterior tubercles, and section. Same 

 horizon and locality. 

 Fig. 4-8. Bataganthus baculiformis, St. J. and"W. 469 



4 a. Side view of a nearly entire spine, showing the swollen extremity armed with strong 



tuberculose processes; 4 b, enlargement of one of the large spinose tubercles of 

 the upper extremity ; 4 c, d, enlargement of tubercles from upper and middle por- 

 tion of the spine ; 4 e, tubercles from the posterior portion ; 4/, transverse section. 

 Keokuk limestone; Keokuk, Iowa. 



5 a. View of the anterior face of a fragment of a similar but worn specimen. Same horizon 



and locality. 



6 a. Side view of fragment of a large specimen ; 6 b, c, d, enlargements of tubercles from 



the anterior, middle and posterior portions of the spine, and profile outlines of the 

 same ; 6 e, transverse secticn. La Grange, Missouri, in the same horizon. 



7 a. Side view of fragment of a small spine, showing the base and outline of internal cav- 



ity. Same horizon, St. Francisville, Missouri. 



8 a. Fragment of the upper extremity of a large spine, probably referable to the above 



form. Same horizon, Nauvoo, Illinois. 

 Fig. 9. ClEXACANTHUS PUGIUKCULUS, St. J. and TV 430 



9 a. View of posterior face of spine, twisted towards the extremity so as to bring into 



view portion of one of the lateral faces, base imperfect; 9 b, transverse section; 



9 c, enlargement of a section from near the middle of the spine, showing the char- 

 acter of the ornamentation in the lateral face. St. Louis limestone; St. Louis, 

 Missouri. 



Fig. 10. Geisacaxthus btellatus, St. J. and TV 440 



10 a. Side view of a nearly perfect spine; 10b, en^rgementof anterior border near insertion; 



10 c, section of the posterior face near the middle, slightly enlarged; 10 d, enlarge- 

 ment of portion of lateral face, showing the disposition of tubercles and faint 

 costa?. with profile outlines of tubercles; 10 e, transverse section near middle of 

 spine, natural size and enlarged. St. Louis limestone; St. Louis, Missouri. 



Fig. 11. Fragment of an undetermined ichtbyodorulite (?). Upper Burlington limestone; Louisa 

 count v, Iowa. 



