1895.] NATURAL SCIENCES OF PHILADELPHIA. 285 



beyond the incisors and the rostrum is broad, blunt and parallel- 

 sided; (4) the frontals are very narrow; (5) the parietals are nar- 

 row, linear and do not extend to the orbits: (6) the supraoecipital 

 does not extend upon the top of the skull; (7) the lower jaw is large 

 and strong; (8) the skull is massive and angular, with well defined 

 ridges and in some species with a sagittal crest. On the other hand, 

 the resemblances to the Heteromyidoe are confined to the. temporal and 

 occipital regions. (1) The greatest width of the skull is across the 

 mastoids; (2) the auditory meatus is inflated and in some species 

 vestibular; (3) the tympanies form large bullae and have the anterior 

 flask-like prolongation found in most of the recent Heteromyidoe, but 

 their apices are more widely separated; (4) the mastoids are largely 

 inflated and appear on the top of the skull, but roof in less of the 

 cranial cavity than iu most of the recent genera; (5) the occiput is 

 almost square and much narrowed by the encroachment of the 

 mastoids. The shape and position of the infraorbital and incisive 

 foramina and the protuberance on the mandible formed by the end 

 of the incisor are as in the modern members of both families. The 

 coronoid process of the mandible is intermediate in character, being 

 larger and higher than in the recent Heteromyidce, smaller and 

 lower than in the Geomyidce. A difference from both is in the shape 

 of the mandibular angle, which is large, falciform and but little 

 • verted. The limb-bones, so far as they are known, resemble those of 

 Thomomys, except for the presence of the third trochanter on the femur. 

 These John Day genera are quite inexplicable except upon the 

 hypothesis that they are ancestral to the Geomyidce ; to regard them 

 as an offshoot of the Geomyidce which have in some respects paralleled 

 the Heteromyidce is a purely gratuitous assumption unsupported by 

 any evidence. The existing Geomyidce are all exclusively subter- 

 ranean and fossorial in their habits, with very small eyes and ears, 

 and in them any extreme delicacy of hearing would be out of 

 place. Further, the inflated mastoids of the existing pocket-gophers 

 are intelligible enough as a character acquired under different cir- 

 cumstances of life and retained now in a reduced degree, while it 

 is difficult to see how such a character should ever be acquired by 

 burrowing animals. Another fact pointing to the same conclusion 

 is that, as Merriam 3 has shown in his admirable monograph, the 



;1 Merriam. C. H. Monographic Revision <>f the Pocket Gophers, etc. U. S. 

 Dep't of Agriculture, North American Fauna, No. 8, Washington, 1895. 



