1877.) 221 
(Cope, 
Measurements. M. 
Diameter of canine tooth (transverse)...............0. 004 
Width of cranium between first premolars.............. -016 
us s fe last molars...............- .030 
The cranium of this species is about the size of that of a large domestic 
cat. 
CYCLOPIDIUS SIMUS. Gen. et. sp. nov. 
Char. gen. Dental formula I. 2; C.4; Pm. +; M. 3 The superior 
canine is small and is separated from the first premolar by a very short 
diastema. First premolar simple, trenchant ; second premolar two rooted, 
with one principal cutting edge; third with an external crescent and a 
rudimental internal one, not united in front. Fourth premolar with the 
inner and outer crescents only, and these well developed. Last true molar 
without heel. Inferior canine with much wider crown than the incisors 
with which it is in close association. First premolar canine-like, but not 
very large ; second premolar simple. Third and fourth premolar with the 
anterior portions trenchant, the posterior with wide or double columns. 
Last true molar with large fifth crescent or column. True molars of both 
jaws prismatic. Symphysis mandibuli codssified. 
Frontal bones much abbreviated in front by a large upwards-looking 
fossa on each side, which are separated by the very narrow and short nasal 
bones. There are lachrymal fosse and a huge foramen in front of them, 
which communicate with the maxillary sinus. There is a prominent trans- 
verse supraoccipital crest, and the otic bulls are greatly inflated. 
This genus is related to Leptauchenia, Leidy, but differs in having but 
two lower incisors below. That genus belongs to a lower horizon, the mi- 
ocene of White River, while the present form is its successor in the upper 
Miocene or Loup Fork beds. The remarkable character of the vacuities in 
the superior region of the front part of the cranium, reminds one of the 
existing genus Sega. Dr. Leidy partially described a similar structure in 
Leptauchenia. In this genus what are clearly nasal bones in Cyclopidius, 
he terms frontals, probably by error. 
Char. Specif. This animal is rather larger than either of those above 
described, and is represented in my collection by one nearly complete cra- 
nium, one entire left maxillary bone, and the under jaws of five, and prob- 
ably of several other individuals. 
The skull is wide and abbreviated in front. The maxillary bones are 
everted on each side of the external nares. The malar bone is very wide 
or deep, and sends upwards a strong postorbital process, which is broken 
off in part, but which probably completed the orbit. The superior facial 
fosse reach backwards nearly as far as the middle of the orbit. They are 
longitudinal narrow ovals, open in front. The projecting supraorbital por- 
tions of the frontal bone with the nasals have a tripodal form. The lach- 
rymal fossa looks outwards, upwards and forwards, and the large maxillary 
foramen outwards. The infraorbital foramen is double, and issues above 
the contiguous portions of the third and fourth premolars. 
