No. 2.] Allen on Mammals from Texas and Mexico. 227 



species, the following differences are to be noted. Besides the 

 general difference in coloration already noticed, the tail in D. 

 sennetti is broadly and continuously blackish both above and 

 below, with the white lateral stripes sharply defined ; in D. ordii 

 the basal half of both the upper and lower surfaces of the tail is 

 so much mixed with whitish as to produce a general grayish 

 effect ; the ears in D. sennetti are broadly edged with blackish on 

 the outer anterior border, of which marking there is barely a trace 

 in D. ordii. But these differences may be seasonal, the El Paso 

 specimen having been taken in December and the Cameron 

 County example in March. There is apparently but little differ- 

 ence in general size or proportions, except in the size of the ears, 

 which are much the larger in D. sennetti. A comparison of the 

 skulls, however, shows surprising differences. In D. ordii the 

 skull is more triangular, the rostral portion being narrow, pointed 

 and rather short, while the mastoid portion is greatly swollen. 

 Just the reverse of this occurs in D. sennetti, the rostral portion 

 being both elongated and broadened, while the mastoids are much 

 less inflated and widely separated by an interparietal area three 

 times as broad as in D. ordii and of an entirely different shape. 

 The interparietal in D. ordii is subtriangular, and nearly three 

 times broader at its anterior than at its posterior edge ; while in 

 D. sennettiti\z interparietal is slightly hour-glass shaped quadrate, 

 slightly hollowed on the lateral margins with the anterior and 

 posterior width about equal. The expanded orbital bridge of the 

 maxillary is broader and much more developed in D. sennetti than 

 in D. ordii. The lower jaw is also very different in the two spe- 

 cies, in D. sennetti the condylar portion being much more de- 

 pressed and the condyle itself longer and very different in form 

 from the same part in D. ordii, while the angle is much broader 

 and its plane less oblique to the vertical plane of the ramus. 



D. sennetti differs from D. compactus in being a'bout one-third 

 larger (judging from the skulls), and in its very much darker 

 coloration. In other words, D. compactus. is a small, pale form, 

 probably restricted to Padre Island. 



30. Tatusia novemcincta (Linn.). One specimen, Tampico, 

 Mex., June i, 1885, J. M. Priour. 



