PLATE VIII. 



PAGE. 



XYSTRODUS INCONDITUS, St. J. and W 179 



Fig. 1 a. Maxillary posterior tooth, left ramus, view from above, outline restored; 1 

 b, do., profile from antero- lateral border; 1 c, do., transverse section. 

 Keokuk limestone; Warsaw, Illinois. Professor Worthen. 



XYSTRODUS IMITATUS, St. J. and W 180 



Fig. 2 a. Maxillary posterior tooth, right ramus, from above; 2 b, do., longitudinal 

 profile from antero-lateral border; 2 c, do., transverse section. St. Louis 

 formation; Monroe county, Illinois. Professor Worthen. 



XYSTBODUS BELLULUS, St. J. and W 183 



Fig. '-i a. Maxillary posterior tooth, left ramus, from above, outline restored; 3 b, do., 

 longitudinal profile from the antero-lateral border; 3 c. do., transverse 

 section. Coal No. 7, 111. Gen'l. Sec; Danville, Illinois. Mr. Wm. Gurley. 



XYSTBODUS SIMPLEX, St. J. and W 178 



Fig. 4 a. Mandibular posterior tooth, left ramus, view from above; 4 b, do., antero- 

 lateral border; 4 c, do., from postero-lateral border; 4 d, do., inner mar- 

 gin; 4 e, do., outer inrolled margin. Upper Burlington limestone fish- 

 bed; Monmouth, Illinois. Mr. Springer. 



Fig. 5 a. Maxillary posterior tooth, right ramus, from above, outline restored; 5 b, 

 do., from the antero-lateral border; 5 c, do., postero-lateral border; 5 d, 

 do., transverse profile from inner margin; 5 e, do., outer inrolled ex- 

 tremity. Upper Burlington limestone, fish-bed; Louisa county, Iowa. 

 Mr. Springer. 



XYSTRODUS VEEUS, St. J. and W 181 



Fig. 6 a. Mandibular posterior teeth, left ramus, view from above; 6 b, do., antero- 

 lateral border, longitudinal profile; 6 c, do., transverse profile from 

 inner margin; Chester limestone; Chester, Illinois. Professor Worthen. 

 Fig. 7 a. Maxillary posterior tooth, left ramus, from above; 7 b, do., longitudinal pro- 

 file from the antero-lateral border; 7 c, do., from the postero-lateral 

 border; 1 d, do., transverse profile from the inner margin. Same forma- 

 tion, locality and collection. 



PCECLLODUS ST. LUDOVICI, St. J. and W 132 



Fig. 8 a. Mandible, with the pair of posterior teeth occupying their natural position, 

 resting upon the granular osseus support, the right ramus showing the 

 articular processes at the extremity. The anterior extremity of the jaw 

 is mutilated, but it is evident whatever teeth it bore were extremely 

 small; St. Louis limestone; Alton, Illinois. Mr. W. C. Van Home. 



Fig. 9 a. Mandibular posterior tooth, right ramus, view from above. Same forma- 

 tion, locality and collection. 



Fig. 10 a. The same form, left ramus, view from above; 10 b, do., outer inrolled mar- 

 gin; 10 c, do., from inner margin. Same formation, locality and col- 

 lection. 



Fig. 11 a. Maxillary posterior tooth, right ramus, from above; 11 b. do., from the outer 

 margin. St. Louis formation; Pella, Iowa. Mr. St. John. 



Fig. 12 a. Same form, left ramus, from above; 12 b, do., from inner margin; 12 c. do., 

 from antero-lateral border, foreshortened: 8t Louis; Alton, Illinois. 

 Professor Worthen. 



