DAKOTA AND NEBRASKA. 2 



LOPHIODON. 



LOPHIODON OCCIDENTALIS. 



This species is founded upon a specimen consisting of a last inferior molar tooth 

 inserted in a small fragment of the jaw, and obtained by Dr. Haj'den in the 

 Mauvaises Terres of White Eiver, in his trip of 1866. The specimen is represented 

 bx figures 28 — 30, plate XXI, and is the only fossil referable to Lophiodon which has 

 been noticed in all the collections from Dakota or Nebraska. 



Characters derived from a tooth cannot always be dej)ended on to determine the 

 genus of animals to which it belonged, and the future discovery of additional material 

 may prove the fossil under consideration to belong to a very different animal from 

 Loj)hiodon. Under present circumstances, however, the specimen can only be appro- 

 priately referred to the latter. 



The crown is composed of a pair of transverse hill-like lobes, as in the lower 

 molars of the Tapir, with the addition of a well-developed posterior conoidal talon. 

 The prmcipal lobes have sub-acute summits, slightly concave transversely. Their 

 posterior surface is sloping, their anterior concave, and their exterior sides are con- 

 vex. The talon is about half the height of the piincipal lobes, convex posteriorly, 

 and with the anterior surface inclining from the middle on each side. The crown is 

 bounded in front by a basal ridge. 



The diameter of the crown antero-posteriorly is nine and three-quarter lines; 

 transversely six and a half hues. 



PROBOSGIDEJE. 



The family of the great proboscideans is represented in the pliocene fauna of the 

 Niobrara Eiver of Nebraska by a species of Mastodon, strikingly distinct from that 

 of a later period, whose remains have been found so abundantly distributed through- 

 out the North American continent. Associated with it there have been discovered 

 the remains of an Elephant, which, especially on account of its relative age, but also 

 from its comparative size, I have suspected to be a distinct species from its American 

 congener of the quaternary period, usually regarded as the Elephas primigenius. 



The remains of the Niobrara Mastodon and Elephant occupy the uppermost of the 

 beds of the tertiary formations of Nebraska, marked in Prof Hayden's tables as 

 bedF. 



In the chapters on the Mastodon and Elephant I have iutroduced some remarks 

 on remains of these genera occumng throughout North America, and have jiresented 

 strong evidence that at least three, and perhaps four distinct species of the former 

 inhabited this continent at different periods. 



