284 



Measurements. 



M. 



Leugtli of the fragment 0.094 



Length to the outer area 0. 031 



Length to the inner area 0. 041 



Width of the inner area 0.029 



Width at the inner area 0.038 



Width of the outer area 0.004 



Grfeensand of New Jersey, No. 5. 



ISCHYODUS, Egerton. 



The species of this genus are numerous in the greensand of New 

 Jersey, but have not yet been met with elsewhere in North America, One 

 occurs in the Eocene formation of the same State, which is nearly allied to 

 the Cretaceous forms. The species may be distinguished as follows : 



I. Dentinal areas very small ; the inner represented by two 

 columns, widely separated from each other: 

 Form compressed ; grinding-face vertical be- 

 hind — . . . — 7. stenobryus. 



1 1. Dentinal areas moderate; the inner represented by three 

 adjacent areas : 

 Inner area inside of margin ; outer margin with 



tuberosities ... I. tripartitus. 



III. Inner dentinal area undivided : 



A Inner area contracted, and separated by a plane from 

 the inner margin : 



Anterior outer on a prominent ledge — / longirostris. 



A A. Inner area extending to inner margin of superior 



face of mandible : 



13. The anterior outer area produced anterior to 



the inner area: 



External areas on laminar crests of the border : 



posterior area very small: anterior cresl 



produced I. Uderigerus. 



Each of the outer areas produced, ami standing 

 on a horizontal step of the thin outer 

 margin /. smockii. 



