7i6 The American Naturalist. [August, 
Agathaumas sylvestre Cope, 1. c. 
POLYONAX MORTUARIUS CopC, 1. C. 
MoNOCLONius RECURVicoRNis Cope, sp. nov. Dinosaurian Cope 
(Bulletin U. S. Geological Survey Terrs. III., 1877, page 588; plate 
34, figures 7 and 8.) 
I excavated the bones of the skull of this species in Montana, and 
described them as above ; but suspecting that they might belong to 
some of the species already known, I did not name them. The fortu- 
nate discovery by Prof. Marsh enables me to determine them. The 
supraorbital horns are robust, straight, and rather short. Their section 
is an anteroposterior oval at base, and at the middle rounded subquad- 
rate. The nasal bones are wedge-shaped and much narrowed for- 
wards; they support a coossified median septum below. Superior 
face rounded, very rugose. Some distance posterior to the apex they 
support a very robust horn, which is compressed and turned abruptly 
forwards at the apex. Posterior face injured. Length of supraorbital 
horn 210 mm., long diameter at base 115 mm.; width of nasal bone 
at base of horn 100 mm.; diameter of nasal horn at base (transverse) 
95 mm.; elevation (on curve) to broken apex, 115 mm. Between the 
supraorbita\ horns on each frontal bone a low tuberosity. This was a 
colossal animal and of peculiar characters. The squamosal is narrower 
than in M. crassus, and had marginal tuberosities. 
parts of the skeleton, including parts of the skull, which were found by 
Charles H. Sternberg, on the Missouri River, near Cow Island, in 
1876. The end of the muzzle is preserved, and presents characters 
which show that the species is quite different from the one last 
described. The nasal bones are greatly produced to form a slender, 
compressed, decurved apex, with a prolongation of the inferior me- 
dian ethmoid septum. The superior face is round in the transverse 
.section, and is rugose. At a long distance behind the apex the nasal 
horns rises. It is compressed and vertical in direction, and was not 
less than 250 mm. in length, but the apex I have not yet found in the 
packages. Supraorbital horns unknown. The nasal bones are nar- 
rower at the base of the horn than in the recurvicornis, and the horn 
is of different form. The anterior border converges regularly to the 
posterior, and its anterior edge is acute for the distal half. Length 
of nasals in front of horn, 255 mm.; transverse diameter of nasals 
below at base of horn, 70 mm.; diameters of base of horn, antero- 
