1884.] o4cl [Cope. 



This genus is Leptauchenia without superior incisor teeth, and with but 

 two on each side below. I originally asserted the presence of superior 

 incisor teeth, and it is true that there is in early life a minute tooth in each 

 prernaxillary bone, as indicated by the alveoli in a specimen which con- 

 tains the full deciduous molar dentition. I have not seen the teeth them- 

 selves, and it is evident that they are early shed. In an adult specimen 

 of G. simus it seems that the alveolar portion of the prernaxillary bone has 

 been absorbed. 



The meatus auditorius externus occupies a more elevated position in 

 this genus than in any other of the family. It is also directed somewhat 

 posteriorly. There are postparielal foramina. 



The cerebral hemispheres are not large, and scarcely rise above the 

 plane of the summit of the large cerebellum. Convolutions three on each 

 side, weakly denned. 



The concavity of the superior border of the prernaxillary bones, to- 

 gether with their upward production, leads me to suspect that the exter- 

 nal nares were superior in position. This is the indication of an aquatic 

 habit of life, such as is led by the hippopotamus. Like that animal, the 

 nostrils in Cyclopidius were probably valyular to prevent the ingress of 

 the water. The animals probably passed much of their time in the water, 

 and the nostrils could be brought to the surface for the purpose of respira- 

 tion, while the remainder of the head and body remained concealed. The 

 prominent rim of the auditory meatus suggests a similar valvular closure 

 of the organ of hearing, and is also a provision for its easy approximation 

 to the surface of the water when necessary. 



The milk dentition is like that of Artiodactyla in general. That is, in 

 the superior series the third molar is more elongate and complex than its 

 permanent successor, and the fourth is like the first permanent true molar 

 in constitution. In the inferior series the anterior three teeth resemble 

 the permanent premolars, while tJae fourth is trilobate. 



In the loss of the incisor teeth and the subprismatic molars, we observe 

 in Cyclopidius the same evidences of specialization already known in other 

 types of Ungulates. 



I know of but two species of Cyclopidius. 



Cyclopidius simus Cope. 



Proceedings American Philosophical Society, 1877, p. 221. Brachy- 

 meryx feliceps Cope, Ibidem, p. 220 (immature). 



The specimens of this species in my possession embrace a complete 

 skull with one zygoma and half of the brain-case wanting ; a left maxil- 

 lary bone with all the teeth ; and three mandibular rami with dentition, 

 all of adults. Of immature individuals, I have two muzzles with denti- 

 tion of both sides, and six mandibular rami ; in all, parts of thirteen in- 

 dividuals. The following description of the skull is taken from the speci- 

 men first named, which is the type of the species. 



The cranium is wide and depressed, and the muzzle is short. The pro- 



