114 Annals of the Carnegie Museum. 



comparison of complete specimens." The reduced nasals, the large 

 anterior nares and air-sinus of Heptodon and Helaletes are specializa- 

 tions of an early origin, which obtained not only in these genera, but 

 in all likelihood was also extended to the true ancestors of the recent 

 tapirs, and may thus be regarded as an additional proof of the con- 

 servativeness of these Perissodactyls. 



Not only did Helaletes have the abbreviated nasals, but the incisors 

 were of subequal size, P- much reduced, and in Heptodon we have the 

 long cursorial limbs, truly a combination of specializations too con- 

 flicting and requiring too great a modification to fit them to be regarded 

 as the true ancestors of the recent tapirs, even be they so far removed in 

 time as the Eocene. On the other hand we have in the genus Colodon 

 of the Oligocene a form which appears eminently fitted to represent 

 the line of pseudo-tapirs in the later Tertiary, according to the deter- 

 minations already reached by Osborn, Wortman, and Earl. 



Dilophodon should only be provisionally included in the sub-family 

 Helalitince, since it is too imperfectly known, and may still prove to 

 be more closely related to the true tapirs. 



When these pseudo-tapirs of the American Eocene are referred to 

 as Lophiodonts it should be in a super-family sense (Lophiodontoidea), 

 although with a greater restriction than that proposed by Dr. Gill.^" 

 In persisting in regarding these American genera as belonging strictly 

 to the European family Lophiodontidse^^ the taxonomy of the whole 

 group is confused rather than cleared. That there is a relation be- 

 tween the European and American forms in question is not to be 

 denied, especially when their dental structure is considered. But is 

 this similarity much greater than that in other separate families; 

 e.g., the Palaeotheres, the Chalicotheres, and the Titanotheres? 

 When comparison of the limb structures of Lophiodon (L. isselensis)^'^ 

 and Heptodon or Helaletes is made we meet with an important degree 

 of adaptive radiation. In Lophiodon, as is well known, the limbs are 



"' See Amer. Jour. Sci., Vol. IV, 1897, p. 161, Fig. 2; Bull. Amer. Mas. Nat. Hist., 

 Vol. VII, 1895, p. 370; Me7n. Amer. Mtis. Nat. Hist., Vol. I, 1898, p. 128a, PI. 

 Xllla. 



8" Smithsonian Mis. Coll. No. 230, 1872, p, 88. Certain genera of suids, anoplo- 

 theres, and Cory phodon, -which were included by Dr. Gill, should, of course, be ex- 

 cluded. 



81 Osborn, H. F., and Wortman, J. L., Bull. Amer. Mus. Nat. Hist., Vol. VII, 

 189s, p. 358; Osborn 's "Age of Mammals," Classification Table, p. 557. 



82 Filhol, M. Henry, Mem. Soc. Geol. de France, Tom. V, 1888. 



