RODENTIA GEOMYINAE GEOMYS BREVICEPS. 



379 



Measurements. 



As stated, this species exhibits considerable resemblance in color to G. bursarius from St. Louis. 

 The tint is, however, more uniform on the back and sides, without the concentrated wash on the 

 dorsal region. The color is rendered deeper, too, by the darker tips to many of the hairs. Beneath, 

 the colors are more grayish, and the whole lining and edges of the cheek pouches, with the throat 

 and chin, are whitish, instead of showing a good deal of chestnut. The inequality in the position 

 and length of the digits is much greater ; thus, in the St. Louis animal, the 2d finger is not 

 much shorter than the fourth, though its claw is much smaller ; in this the claw, even of the 

 second finger, reaches but little beyond the end of the fourth finger. The greatest differences 

 are, however, discernible in the skulls. In the present species they are broader in proportion ; 

 especially behind, and the widest portion of the zygomatic arch, instead of being at the end of 

 the zygomatic process of the upper maxillary, with the zygomata converging in straight lines 

 behind this point, is really considerably further back, owing to the greater extension laterally of 

 the zygomatic process of the temporal with the convex outlines of the zygomatic arch. The 

 forehead is much flatter and the snout shorter. The teeth are also different ; the isthmus between 

 the lobes of the anterior upper molars, instead of connecting the middle of these lobes, passes 

 inside of the middle, exhibiting a shorter sinus inside than out. The posterior upper molar is 

 more rounded or nearly circular with the angles obsolete. The molars of the lower jaw are 

 much larger, especially the anterior one. The coronoid process stands a good deal higher and 

 its axis more vertical. 



The skull of the present species resembles quite closely the one figured by Waterhouse in 

 Charles worth's Magazine as Geomys umbrinus. 



The absolute determination of the species of Geomys, as of many other American animals, is 

 a matter of much uncertainty, in consequence of their wide range, and the difficulty of getting 

 enough materials for satisfactory comparison. Since the article on G. breviceps was written, I 

 have had the opportunity of examining several other specimens, probably referrible to this 

 species, from quite remote localities. One of these, from western Texas, Llano Estacado, col 

 lected by Captain Pope, is quite similar in every external character, but the teeth are narrower, 



