280 PROCEEDINGS OF THE ACADEMY OF 



before me skulls of all the described North American species ex- 

 cepting fasciatus. They are so nearly similar, that description of 

 one "will suffice for all, barring some slight ultimate details of 

 size, etc. I select that of P. penicillatus for description, omitting 

 generalities already presented. The description may be compared 

 with that of Dipodomys given beyond. 



Although the temporal bone is largely developed in the mastoid 

 element, that lacks the enormous inflation seen in Dipodomys, the 

 general shape of the skull being not dissimilar to that of several 

 allied rodents. Nevetheless the mastoid represents the postero- 

 exterior aspect of the skull, and is large enough to crowd the 

 squamosal into the orbit, and cause a slight protuberance bej'ond 

 the actual plane of the occipital bone. But this is insufficient to 

 produce even the moderate emargination of this surface witnessed 

 in Cricetodipus, and is nothing at all like the regular cleft or 

 chink seen in Dipodomys. The ends of the petrosals are fairly 

 separated by the width of the basisphenoid ; they lie in contact 

 throughout with the basioccipital, and show a conspicuous for- 

 amen posteriori}- on the inner side. The meatus auditorius ap- 

 pears as a mere flange-like projection, intermediate in character 

 between the swollen vestibule of Dipodomys and the contracted 

 tube of Geomyidve, though nearest the latter. The occipital is 

 broader than in any other genus of the family, the forks which 

 embrace the interparietal being fairly laminar, instead of mere 

 spurs. The interparietal is much wider than long. The parietals 

 are almost perfectly pentangulai'. A slight spur of the squamosal 

 pushes out toward the meatus, but does not extend as a long clasp 

 over the tympanic ;' the squamosal is otherwise wholly orbital. 

 The frontal is quite flat on top, squarely and straightly truncate 

 behind, serrate in front for articulation with the rostral bones, 

 and with straight sides convergent posteriorly. There is a large 

 lachrymal of wholly irregular shape, extensively scroll-like, very 

 delicate in texture, and loosely attached ; it closes a large aper- 



1 In a specimen of Cricetodijms, I clearly see that a long slender spur is 

 scut out from the squamosal, like a clasp or hasp, lying above and reach- 

 ing back of the meatus. Cf. what is said of an apparently similar, but 

 not well made out appearance in Dipodomys, beyond. It is, in this case, 

 a slender remnant of squamosal bone, left in an ordinary place, after most 

 of the bone has been shoved into the orbit by the encroachment of the mas- 

 toid. 



