297 



previously described, being less symmetrical than the large teeth and more 

 so than the smaller ones, and their crown is proportionately more prominent 

 than in any of them. Of three teeth smaller than the former and succes- 

 sively diminishing, that of intermediate size is represented in Figs. 7 and 8. 

 They have the same form as the unsymmetrical ones of the first parcel, but 

 have their crown proportionately much more prominent. 



The remaining two teeth are different in shape from the former. The 

 larger one has the crown proportionately less prominent, with the central 

 conical elevation less strongly radiate. The inner side of the base forms an 

 obtuse angle, and is strongly impressed toward the back border. The front 

 border of the base of the crown is short, nearly straight, and forms with the 

 oblique outer border an obtuse angle. 



The smaller tooth is represented in Figs. 9 and 10, and has nearly the same 

 shape as the former, but the crown appears comparatively flat with a central 

 nipple-like eminence, and the anterior and outer borders are more continuous. 



The measurements of the teeth are as follows : 







Figs. 

 5, C. 





Figs. 



7,8. 







Figs. 

 9, 10. 



Breadth of crown transversely 



Breadth of crown antero-posteriorly . . 

 Height of crown from bottom of root. . 



Lines. 



7 

 10£ 



Lines. 

 14 

 8 

 94 



Lines. 



G 



S 



Lines. 



5 

 C 



Lines. 



7 

 4 

 4 



Lines. 



10 

 



Lines. 

 ■ 7 

 U 

 H 



Several specimens of teeth of Plychodus Mortoni have been submitted to 

 my inspection by Dr. William Spillman, who obtained them from the Creta- 

 ceous formation hear Columbus, Mississippi. One of the teeth, of large size, 

 and considerably worn at the summit of the crown, is represented in Figs 

 11 and 12. It is symmetrical in shape, but has a more reniform outline than 

 the large teeth from Kansas. The anterior and lateral borders of the crown 

 nearly form a semicircle, and the posterior border is deeply emarginate. 

 The sinus is deeper than- in the Kansas specimens, but the arrangement of 

 the striatums of the crown appear to be the same. 



Two other specimens, about half the size of the preceding, have nearly the 

 same shape, but have their crown proportionately more convex at the fore 

 part of the base. 

 38 G 



