PAL.EOSYOPS LEIDY, AND ITS ALLIES. 
273 
lies of the Perissodactyla, that in his first paper upon this snljject' he did not sub- 
divide the family Menodontidce from the ChalicotheriidcB . lie included the genera 
Pal(eosyops and Menodus 0.11 under the fiunily Chalicotheriida:, and he follows this 
arrangement in his second paper upon the classification of the Perissodactyla.^ In 
his third paper upon this subject Professor Cope, for the first time, separated the 
Menodontidce from the Chalicolheriidce, basing the differential characters of the two 
families ni)on the simplicity or complexity of the jjremolar series respective!}’. Both 
Schlosser and Osborn® have noticed the close affinity between Palceosyops, Diplacodon 
and Titanotherium, and consider that on account of the transition characters of the 
preraolars t)f Diplacodon, the three genera in question should be united into one 
family. Lydekker,^ in his Manual of Palasoutology, follows Cope in the arrangement 
of this family, including in it the genera Palceosyops and Titanothermm, and placing 
Chalicotheriurn in a distant family of the Perissodactyla. I should also add that 
Lydekker jjlaces Palceosyops in the family Lambdotlieriidce proposed by Cope. Stein- 
maiin and Dfoderlein'^ form three suljfamilies for the genera Palceosyops, Titanother- 
ium {—Bronlotheriiim), and Ckalicotheriuni Ye\i\iQQXivii\y , condjining these all in the 
family Chalicotheriidce. After considering the question of the union of these genera into 
one family, I quite agree with Osborn and Schlosser, and see no real line of family 
di.stinctiou between them. I think that Palceosyops and allied genera, Diplacodon 
and lastly Titanothermm, should be placed in the family Titanotheriidce, proposed 
by Osborn." 
It appears to me that the arrangement proposed by Doederlein, of placing the 
genera of this family into subfamilies, is a very good one, and I shall accordingly 
follow it. ^ . ' 
General Characters of the family Titanotheriidce. — The family Titanotheriidce 
may be defined as follows : Skull elongated, with zygomatic fossa prolonged beyond pos- 
terior limit of molars. OiLit small and not separated from temporal fossa behind. 
Nasals elongated and reaching at least as far as premaxillary symphysis. Lateral 
nasal notch deep. Nasals with or without horns. Auditory processes Avell developed. 
Postglenoid process large. Occiput broad with prominent descending paroccipital 
2 )rocesses. Alisjjhenoid canal much elongated. Foramen ovale distinct and widely 
separated from the for. lacerum medium. Tympanic bone not coossified with petrous. 
Superior molars of the buno-selenodont type, with symmeti’ically developed external 
A^’s, separated by a prominent median buttress. Internal cones of molars separated 
from external lobes. Intermediate tubercles generally well developed. Lower 
molars of the lopho-selenodont type, consisting of double V’s, with the posterior crest 
■Bull. r. S. Geol. Surv., 1879, p. 228. 
“Am. Xat. April, 1881, p. 340. 
“Uinta Mammalia, p. 141, Aug. 20, 1889, (Trans. Am. Phil. Soc. Vol. 16). 
^Manual of Pateontology, Xicholson and Lydekker, 1889. 
“Elemente der Palaeoiitologie, 2 Band, p. 776. 
“Loc cit. 
