281 



HOLOCEPHALI. 

 LEPTOMYLUS, Cope. 



Proceedings of the Boston Society of Natural History, 1869, p. 313. 



Three species of this genus are known to the writer, which may be 

 distinguished as follows : 

 I. Mandible without apical dentinal cylinder: 



Large, massive, and not compressed . L. densus. 



II. A terminal or apical cylinder: 



Outer margin much elevated; inner much depressed; large.- L. forfex 



Outer margin less elevated; the inner equally so; smaller. . . L. cookii. 



Leptomylus densus, Cope. 



Proceedings of the Boston Society of Natural History, 1869, p. 313. 



Greensand of New Jersey, No. 5 ; Birmingham, Judson Gaskill. 



LcPTOMYLUS FORFEX, Cope, sp. UOV. 



This chimasroid is represented by two mandibles from distant localities, 

 and probably by a maxillary bone. The form of these elements is highly 

 characteristic. The mandible is much elevated ; but the elevation is confined 

 to the outer side, which rises as a lamina, causing the masticating face to be 

 nearly vertical for much of its length ; but a short extent is level to the apex. 

 There is a slight marginal swelling where the anterior outer dentinal area 

 should be, and an abrupt rise in the margin to the position occupied in 

 Ischyodus by the posterior outer area. The inner border of the masticating 

 surface is parallel to the inferior border of the jaw, except where the two 

 converge to the apex ; here the entire face included between them is occupied 

 by the large symphyseal facet. The inner dentinal area is represented by a 

 narrow acuminate patch on the inner angle of the masticatory face, opposite 

 the tuberosity which represents the anterior outer. The apical area is very 

 narrow, and extends for some distance along the exterior angle of the 



superior face. 



Measurements. 



if. 



Length of a fragment 0. 13|5 



Length to the posterior outer tuberosity : 0. 066 



Depth behind 0.102 



Depth at the anterior outer tuberosity 0. 055 



Depth of the inner face behind J 0. 031 



Length of the inner dentinal area * 0. 014 



Width at the inner angle (behind) 0. 023 



Width near the superior border 0. 013 



36 c 



