424 THE PUERCO EPOCH. 



PROTOGONIA Cope. 



Paleontologic.ll Bulletin, No. 3:{, p. 492, Sept. 30, 1881. Proced. Amer. Philos. Soc, 1881, p. 4"J2. 



Fourth superior premolar with one external and one internal lobe. 

 Ti-ue molars with two external, two internal, and two intermediate lobes, 

 both the latter connected with the anterior internal by a ridge. Supposed 

 inferior true molars with two V's with weak anterior branches; last true 

 molar with heel. Fourth inferior premolar with internal cusp. 



In the superior true molars the anterior transverse crest of the Hyra- 

 cotherium is represented, but not the posterior. This is replaced by a low 

 ridge running across the course it pursues in Hyracotherium. The posterior 

 median tubercle is also not found in the latter genus. Protogonia differs 

 from Limuohifus in the subconic character of the external lobes of the su- 

 perior molars. If the tubercles, excepting the posterior inner, should be 

 converted into crescents, the genus Me)mcotherium would be produced. It 

 probably represents the ancestral type of the Meniscotheriidai. The simple 

 premolars give it a position nearer the Periptyckidae than that occupied by 

 Phenacodus. Xx\ approach to it is made by tlie Phenacodus puercensis of the 

 same geological horizon. Two species of Protogonia are known to me. 



Protogonia plicifera Cope. 



Ameticau X.itiirali.st, lr<82, p. 833 (Sept. 28). 

 Plate XXV/; lij;s. 2-3. 



This species, although not the first described, is most expressive of the 

 characters of the genus. The external lobe of the fourth superior premolar 

 is absolutely simple, as in most Artiodactyla, while in the P. subquadrafa 

 there is a minute rudiment of the second or posterior external cusp, which 

 is well developed in Phenacodus. A single individual is all that is known 

 of the species. This is represented by a maxillary bone, which contains 

 the fourth premolar, and anterior two true molars, and the accompanying 

 mandibular ramus, which supports the three corresponding inferior teeth. 



This species is smaller than the P. subquadraia, and differs from it es- 

 pecially in the form of the internal cusp of the fourth snj)erior true nitjar. 

 In this species it is the apex of a V, whose limbs form tlie anterinr and 

 posterior cingula. In P. subquadraia it is a simple cone, disconnected from 



