1896.] -•-*< [Farr. 



JVotes on the Osteology of the White River Horses^. 



By Marc^is 8. Farr. 



{Read before the American PhilosopJiical Society, May 15, 1S96.) 



MESOHIPPUS. 



Although nearly half a century has elapsed since MesoJiip^ms hairdi 

 was first described by Leidj',* our knowledge of its osteology has 

 remained comparatively incomplete, all the known material being lim- 

 ited to foot bones and more or less complete skulls. Most all of the 

 skeletons that were found were badly broken up and only the larger 

 and more perfect bones were saved. Modern methods of collecting, 

 essentially those introduced by Mr. J. B. Hatcher,f have revolutionized 

 all this and now even the most delicate bones, though badly broken up, 

 are preserved as easily as the large bones were before collecting was 

 done in a scientific manner. 



Fortunate discoveries of more complete skeletons during the last three 

 years have given us very much better material and now enable us to 

 supplement the accounts of M. bairdi that have already been given, to 

 add many new points on the osteology of the species and to oft'er a 

 restoration which is an improvement on those heretofore oft'ered. 



Several species of Mesohippus have already been made on material 

 fi"om Nebraska, Dakota and Colorado. These have either been founded 

 on a few teeth presenting peculiarities or on foot bones not associated 

 with teeth. These species have not been generally accepted, and the 

 founding of species on such limited material especially in such a genus 

 as Mesohippus which presents such a marked degree of individual varia- 

 tion does not seem justifiable and merelj^ burdens science with useless 

 synonyms. I have not seen the types upon which the various species, 

 31. exoletum,X M. agrestis,% M. cu)ieatns,\\ M. celer,^ etc., have been estab- 

 lished, but from the study of the individual variations in the many** 

 specimens of M. bairdi studied by the writer it seems very evident that 

 the species are not well grounded and that the peculiarities may be 

 accounted for by the factor already mentioned. 



The discovery of the Protoceras beds and their recognition as a dis- 

 tinct subdivision of the White River formationsf f marks a stage in the 

 development of the palaeontology of this epoch. 



*Leidy first described this species as Palxotherium bairdi, Proc. Acad. Nat. Sd., 1810, 

 p. 122. 



+ Curator of Vertebrate Palaeontology in the College of New Jersey. 



tCope, U. S. Geol. Survey of the Teiritwies, 1873. 



§Leidy, Kept. U. S. Geol. Sur. Terrs. (4to), i, p. 251, PI. vii. 



II Cope, Palseontl. Bull., No. 16, p. 7, August 20, 1873. 



H Marsh, Am. Jour. Sci. and Arts, 1874, p. 251. 



•* Remains of nearly one hundred individuals have been studied by the writer. 



+t Wortman, On the Divisions of the White River, Ball. Am. Mus. Nat. Hist., Vol. v, pp. 95- 

 100. 



PROC. AMER. PHILOS. SOC. XXXV. 151. S. PRINTED SEPT. 2, 1896. 



