RODENTIA—SCIURINAE—CYNOMYS., 329 
CYNOMYS, Raf. 
Cynomys, Rarinesque, Am. Month. Mag. IJ, 1817, 45. 
Branr’s Muizen,. 1827, 171. 
Antsonyx, Rarinesqur, Am. Month. Mag. I, 1817, 45, (Based on an erroneous interpretation of a description by 
Lewis and Clark.) 
Cheek pouches very rudimentary ; tail and ears very short. Five distinct claws to all the feet. Molars very large; their 
lines strongly divergent anteriorly, closely approximated behind. First upper molar as large in horizontal section as the 
second. Skull very broad, the lines of the zygomata strongly convergent anteriorly. Pupil round.? 
The prairie dogs of America are characterized by various peculiarities which separate them 
from the genera Arctomys and Spermophilus, although they have been placed in both. The 
genus Cynomys was established by Rafinesque, in 1817, and has priority even over Spermophi- 
lus.‘ In the character of the cheek pouches the resemblance to Arctomys is much closer than to 
Spermophilus ; these are (in the alcoholic specimen) about one third of an inch deep and very 
shallow, very little deeper, if at all, than what is observable in the Arctomys monax. In Sper- 
mophilus, on the contrary, the pouches extend back as far as the eyes, and even, in some species, 
to the occiput. The thumb, though short, is quite distinct and carries a well developed claw. 
The tail is short, from one-fourth to one-seventh the length of the body. 
The skull of Cynomys is remarkably broad and short, the extreme width equal to the length, 
exclusive of the snout. The muzzle is slightly compressed and quadrangular. The nasals are 
slightly concave on their external border, narrowing behind; the nasal process of the upper 
maxillary broad, with parallel sides; the suture of the frontal bone, with the maxillary, inter- 
maxillary, and nasal, almost in the same transverse straight line. The dorsal outline of the 
skull is gently convex, the edges of the orbit elevated somewhat, so that a transverse section 
between the orbits would be concave. The post-orbital processes of the frontal bone are very 
highly developed, the posterior border nearly in a straight transverse line, though slightly 
subulate. The cranium is broad and depressed. The posterior extremities of the zygomatic 
arch are much further apart than the anterior, the convergence anteriorly being such that 
the lines would meet at about half the length of the skull, in advance of the snout. 
The free portion of the zygoma is of greater length than in the other Sciwrinae, and the 
direction of the anterior edge of the zygomatic process of the maxillary less oblique. The an- 
terior face of this process is also much more deeply excavated, so that it has a distinct exterior 
and overhanging wall. The ante-orbital foramina are quite large, though far forward ; they 
are elongated and strongly divergent below, so that the thin plate of bone which bounds them 
exteriorly has its edge parallel with that of the zygomatic process of the maxillary. The 
tubercle at the lower end of this foramen is much larger than usual and is distinctly visible when 
viewed from above, projecting beyond the superior outline of the skull, which is not the case in 
any American species of the allied genera. 
The incisive foramina are moderately large and bounded posteriorly by the edge of the max- 
illary, which is considerably nearer the molars than the incisors. The palato-maxillary 
foramina are on the suture of these two bones. In consequence of the great contraction of the 
palate posteriorly, the foramen behind the last molar is very much reduced in size. 
1 Should the two genera be necessarily united, in any event Cynomys would haye to be retained, as having priority. 
42 L 
