i«89-] The Artiodactyla. 135 
is the penultimate or the last premolar. If it is the last, the 
genus Mylohyus will be distinguished by the presence of only 
two premolars. 
An examination of the crania oi Dicotyles tajassus in the 
U. S. National Museum from Costa Rica, shows that they 
display characters intermediate between the Brazilian typical 
form, and the D, angiilatus of Texas. The last premolar 
teeth are sometimes premolariform, and less frequently ap- 
proach the molariform structure. The facial angle is con- 
tinued to the position of the canine aveolus, and the ridge of 
the maxillary bone is only separated from its border by a 
groove, not a fossa. The nasal bones are not tectiform. In 
general the characters agree with the D. tajassus, but the 
lateral facial angle is as in D. angiilatus, and occasionally the 
last premolar resembles that of the same species. It appears 
then that the latter must be regarded as a subspecies rather 
than a species. 
EXPLANATION OF PLATES. 
Plate III. 
Agriocha^r s guyotianus Cope, skull, natural size ; from 
side, and one-half from below. From the John Day Bed of 
Oregon. Original from unpublished plate in Report of U.S. 
Geol. Survey Terrs. 
Plate IV. 
The elbow joint of Mammalia, separated, and seen from 
above and posteriorly. A, Crocuta viandata. B, Siviia nigra. 
C, RJiinolophns sp. D, Eucrotaphus pacificus. E, Cerrus 
elaphns. All four-fifths natural size. 
Vertebra; of Artiodactyla, two-thirds natural size. 
Atitilocapraamericana; 2,Dicotyles angulatus; 3, Capra I 
Prz prezygapoplysis ; Poz postzygapoplysis; E.S. Epis 
