598 THE BRIDGEE EPOCH. 



The pi'emolars differ from the molars in having all their diameters, 

 excepting the vertical, reduced. The fourth premolar only differs from the 

 first true molar in the less elevation of the posterior border of the heel, and 

 in a little smaller transverse diameter. The external part of the heel of the 

 last molar rises into an obtuse cusp ; the remainder of the border is tuber- 

 cular The heels of the other true molars end in simple recurved trans- 

 verse edges. On the premolars their posterior extremities are not recurved. 

 The anterior face of the anterior cross-crest of all the molars is concave, 

 and on the second premolar it looks obliquely inward. The posterior or 

 second anterior inner cusp- is obsolete on the second premolar. The enamel 

 on all of these teeth is, excepting where worn, rather finely wrinkled. The 

 first premolar is not preserved, but its alveolus indicates that it is one-rooted 

 and rather robust. The sizes of the alveoli of the other anterior teeth are 

 arranged in the following order, commencing with the largest : C ; I. 2 ; I. 

 3. The alveolus of the. canine is compi-essed, and has more than twice the 

 anteroposterior diameter of the largest incisor. The alveoli of the first and 

 third are subround ; that of the second is somewhat compressed. 



Measurements. m. 



Length from the middle of the second incisive alveolus to the extremity of the last molar 1950 



Length of the series of consecutive molars 1 170 



Length of diastema 0240 



Diameter of alveolus of Pm. I OO'.tO 



Diameter of alveolus of canine 0250 



Length of premolars 0460 



■ vertical 0130 



Diameters of Pm. II < anteroposterior 0130 



( transverse 0090 



! vertical . .0120 



Diameters of Pm. IV < anteroposterior 0105 



' transverse 0120 



I vertical 0100 



Diameters of M. I.. . < anteroposterior 01.55 



' transverse 0110 



I vertical 0176 



Diameters of M. III< anteroposterior 0260 



( transverse 0180 



The appeai-ance of the ridges of the anterior part of the jaw of the 

 Batliyopsis fissidens, together with the remarkably large dental canal and 

 mental foramen, strongly suggest that the animal possessed a large and 

 perhaps prehensile lower lip. 



From the Wind River, Wyoming. J. L. Wortman. 



