NATURAL SCIENCES OF PHILADELPHIA. 
28 
Castor (Eucastor) tortus, Leidy. 
The greater part of an upper jaw, consisting of tlie upper maxillse and inter- 
maxillse containing the greater portion of the incisors, together with the an- 
terior three molars of both sides, indicates an old individual of a small Beaver. 
The jaw and incisor teeth have the same form as the corresponding part of 
the recent Beaver. The first molars present nearly the same arrangement 
I as in the latter. The succeeding two molars are nearly worn to the base of 
their crown ; and they have the enamel folds on the triturating surface 
directed much more obliquely from the outer side inward and backward than 
they would ever appear to do in the same condition in the recent Beaver. 
The size of the species was about half that of the latter animal. 
Length of space occupied by the series of four molars 6 lines. 
Length of space from first molar to the inter-incisive crest 14 " 
Breadth of face outside of second molars 7 
Diameter of incisors 2 " 
Diameter of first molar 2^ " 
RUMINANTIA. 
".^ERVus Warreni, Leidy. 
This species of deer is indicated by a fragment of a lower jaw containing the 
posterior four molar teeth, portions of two last inferior molars, a small antler, 
and a small fragment of a second. The form of the teeth is the same as in 
Cervus virgmianus, and their size accords with that in full grown and robust 
individuals of this species. The antler is perhaps that of a young animal. 
The frontal process supporting it is half an inch in length and thickness. A 
little less than an inch above the ring of the antler it divides into two diverg- 
ing prongs, of which one is broken off, and the remaining one is two and a 
quarter inches long. 
Length of series of the posterior four lower molars 30 lines. 
The species is respectfully dedicated to Lieut. Gr. K. Warren, U. S. A., com- 
mander of the expedition, during which the remains were collected forming; 
the subjects of the present communication. 
Merycodus necatus, Leidy. j> 
Proc. Acad. Nat. Sci. vii. 90 ; ibid. viii. 89. 
This genus and species were originally proposed on a small fragment of a 
lower jaw of a ruminating animal, belonging to the collection of Prof. Hall, of 
Albany, and discovered by Messrs. Meek and Hay den on Bijou Hill, Nebraska, 
in the summer of 1853. 
The collection from the Niobrara contains the greater ]3ortion of four halves 
of lower jaws, together exhibiting a full series of molar teeth. 
The form of the jaw supporting the teeth is much like that of the Deer, ex- 
cept that its base turns up posteriorly as in the Musks. 
The inferior true molars have much more nearly the form of those of the 
Sheep than of those of the Deer or Musk. The posterior two premolars have 
crowns very much like that of the second premolar of the Deer, and the first 
is like the corresponding one in the same animal. 
Depth of lower jaw at first premolar 6 lines. 
Depth of lower jaw at last true molar 8^ " 
Length of series of six molars 2(3 ' ' 
Length of series of true molars 17 " 
Peo€Amelus occidentalis, Leidy. 
This genus and species are founded on several fragments of jaws, with teeth 
of several individuals of an animal allied to the Camel, and about two thirds 
its size. 
The posterior fragment of a lower jaw presents the same general form as in 
the corresponding part of the Camel, but is broader at the ramus in relation, 
with its height than in the latter. The posterior coronoid process is well de- 
1858.] 
