THE MAMMALIA OF THE DEEP RIVER BEDS. 77 



inflection is hardly at all oblique in its course, but runs nearly parallel to the fore and 

 aft axis of the tooth. In both of the lower teeth represented in the specimen, the 

 antero-posterior diameter of the crown exceeds the transverse, which is very unusual 

 in this genus. The incisors are narrow, with anterior faces which are less convex 

 than in Castor and are covered with a thick layer of orange-colored enamel. 



Two caudal vertebras indicate that this species had a longer and more slender 

 tail than the beaver ; the anterior portion was provided with chevron bones. 



The humerus has a rather slender, trihedral shaft and prominent deltoid ridge, 

 which terminates in a massive overhanging hook ; this hook is proportionately even 

 better developed than in Castor. The supinator ridge is also conspicuous and con- 

 tinues high up upon the posterior aspect of the shaft. The trochlea is low and nar- 

 row, more so than in the beaver, but otherwise shaped as in that animal, and the 

 anconeal fossa is very shallow, not so deep, in fact, as the supratrochlear. The inter- 

 nal epicondyle is very prominent, massive and rugose, and is perforated by a large 

 foramen. 



The femoral trochanters are well developed, but the third is placed more proxi- 

 mally than in 8. peninsulatus or in the beaver. The calcaneum has a short, 

 depressed, irregular and club-shaped tuber; the sustentaculum is notably smaller 

 than in the modern species, and the external projection near the distal end much 

 more prominent ; the cuboidal surface is of triangular outline and slightly concave. 

 Of the metatarsals only the third is preserved in the specimen, but this is sufficient 

 to show that in this species of 8teneofiber, at least, the foot had very different propor- 

 tions from what we find in the existing genus. This metatarsal is relatively very 

 much more slender and shorter than in Castor and of quite different shape, as the 

 shaft is of nearly uniform size throughout, not being contracted in the middle nor 

 expanded distally ; it is also more depressed and flattened, and the head for the first 

 phalanx less enlarged. The proximal end has an oblique surface for the ectocunei- 

 form, which is abruptly constricted behind and continued as a narrow posterior 

 tongue. This specimen suggests very strongly that when 8teneofiber becomes com- 

 pletely known it will prove to be much better distinguished from Castor than the 

 skull and dentition have led us to suppose. 



Measurements. 



M. 



Length of first upper molar 004 



Width of first upper molar 



Length of second upper molar. 

 Width of second upper molar. . 

 Length of third upper molar. . . 



.005 

 .004 



.005 

 .003 



