836 THE WHITE RIVER FAUNA. 



transverse crest from the anterior horn of the anterior crescent is largely 

 developed in both jaws, while that proceeding from the posterior horn of 

 the posterior crescent is united at both ends with the adjacent one. On 

 the last superior molar, the posterior of the two principal cross-crests is 

 shortened, and the posterior marginal crest is cut off from the inner crescent 

 by a notch. In the premolar of the inferior series, the two anterior cross- 

 crests, are wanting and are replaced by two adjacent cusps, an internal and 

 an external. 



The incisive foramina are short and rather wide. There is no tuber- 

 osity on the side of the superior diastema as in most Sciuridce. There is a 

 well-marked fossa above the first premolar, and below the foramen iufraor- 

 hitale exterius. The anterior part of the zygomatic arch is convex above 

 and flat below, and at right angles to the long axis of the skull. An osseous 

 bar extends outwards and backwards from the external base of the external 

 pterygoid ala; whether it spans an alisplienoid canal I cannot determine. 

 The palate is excavated as far as the posterior border of the last superior 

 molar tooth. The ascending portion of the premaxillary bone is wide. 



The area of insertion of the masseter muscle on the mandible, is feebly 

 defined, extending only to the posterior border of the second molar. The 

 pterygoid fossa of the ramus is on the other hand, deeply excavated. The 

 ascending ramus commences opposite the third molar. The dental foramen 

 enters some distance behind the last molar on a level with its summit, and 

 above the angular superior l)order of the pterygoid fossa The mental 

 foramen issues behind the middle of the length of the diastema and above 

 the middle of the vertical diameter of the ramus at that point. 



The section of the superior incisor teeth is a nearly regular oval, a 

 little flattened on the inner side near the front. The anterior face presents 

 a very shallow median longitudinal concavity. The enamel is nearly 

 smooth, andis wrapped on the inner side for a moderate width. The inferior 

 incisors are more oblique on the exterior side anteriorly, and are therefore 

 naiTower in front than the superior. The enamel is smooth, presents no- 

 sulcus, is wrapped in a narrow band on the inner side, and on half the 

 entire width on the outer side. 



There are differences in the form of the inferior premolar, some being^ 



