RODENTIA SCITTRINAE CYtfOMYS. 329 



CYNOMYS, Raf. 



Cynomys, RAFINESQUE, Am. Month. Mag. II, 1817, 45. 



BRANT'S Muizen, 1827, 171. 



Anisonyx, RAFINESQUK, Am. Month. Mag. II, 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. 1 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 Sciurinae, 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 have to be retained, as having priority. 



42 L 



