298 



The measurements of the Mississippi specimens arc as 



follows . 







Figs. 11, 18. 







Breadth of crown transversely 



Lines. 



20 

 10 

 9£* 



Lines. 

 12 



Lines. 



lOg 



7 



Breadth of crown fore and aft 



Heigh t of crown 



7 







. * To worn summit. 



The Museum of the Academy of Natural Sciences of Philadelphia contains 

 nine specimens of teeth of Ptychodus Mortoni from the Cretaceous formation 

 of Alabama. These in general resemble the symmetrical and unsymmctrical 

 teeth above described. One of the specimens from Green County, Alabama, 

 is represented in Figs. 13, 14. Its sinus is more sharply triangular than in 

 the previous specimens. 



Another tooth, approaching in size the largest Kansas specimens, has a 

 more distinct conical ridge on the summit of the crown from which the other 

 ridges radiate. A third tooth nearly resembles the Kansas specimen repre- 

 sented in Figs. 3, 4, and has the summit of the crown worn away, as in the 

 large Mississippi specimen, represented in Figs. 11, 12. 



Measurements of Alabama specimens of teeth areas follows: 



. 





Figs. 13, 14. 









1 



Breadth of crown transversely 



Breadth of crown fore and aft 



Height of crown from bottom of root. . 



Lines. 



16 



10J 



10J 



Lines. 

 9 



Lines. 



16 



9 



Lines. 

 13 



7 

 8 



Lines. 

 9 



Ptychodus occidentalis. 



A peculiar species, to which the above name has been given, is indicated 

 by specimens of teeth discovered by Dr. John L. Leconte in an ash-colored 

 chalk of the Cretaceous formation a few miles east of Fort Hays, Kansas. 



The most characteristic, and at the same time the largest specimen, is 

 represented in Figs. 7, 8, Plate XVII, of the natural size. 



The shape of the tooth and the arrangement of the ridges of the crown 

 are quite different from what they are in the preceding species. The tooth 

 is symmetrical, as in the largest teeth of Ptychodus Mortoni, but it is propor- 

 tionately of less breadth transversely, and also higher. 



