SACCOMYID.E— L'EKOGNATHIDINiE— PEKOGNATHUS. 45)7 



an analysis of the species. I have before ine skulls of all the known valid 

 North American species excepting P. fasciatus. They are so nearly similar 

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

 of size, &c. I select that of P. penicillatus for description, omitting gener- 

 alities 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. Nevertheless, the 

 mastoid represents the postero-exterior aspect of the skull, and is large 

 enough to crowd the squamosal into the orbit, causing a slight protuber- 

 ance beyond the actual plane of the occipital bone But this is insufficient 

 to produce even the moderate emargination of this surface witnessed in Crice- 

 todipus, 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 basisphe- 

 noid ; they lie in contact throughout with the basioccipital, and show a con- 

 spicuous foramen posteriorly on I he inner side. The meatus auditorius 

 appears as a mere flange-like projection, intermediate in character between 

 the swollen vestibule of Dipodomys and the contracted tube of Geomy/dce, 

 though nearest the latter. The occipital is broader than in any other genus 

 of the family; the forks which embrace the interparietal being fairly laminae, 

 instead of mere linear spurs. The interparietal is much wider than long. 

 The parietals are almost perfectly pentangular. A slight spur of the squamo- 

 sal 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 



was right. I quote from Mr. Alston's letter some passages which bear upon the ease, anil show, further- 

 more, with what caution must not Dr. Gray's statements he received: — " The type of Abromys lordi is in 

 had condition, the ears being hopelessly distorted, but it seems to mo to bo undoubtedly P. monticola. 

 P. bicolor Gray, (from Honduras.) appears to be a good species, but has been curiously badly described. 

 It is dark brown above, not black, and tho' the fur is sparse and somewhat harsh, it is not in the least 

 bristly! Gray seems to have had both this specimen and his Reteromys metaiiokucus in his bauds when 

 he wrote and to have confused one with the other. R. desmarestianus Gr. and B. adspersus Ptrs. will 



prove, I fancy, to bo identical Dr. Giiuther has lately got a perfect spirit specimen of R. anoma- 



lus Thomps., so we may expect a full account of its anatomy. As you surmised, Gray's four other 

 species, R. melanoleucus, loiigicaudalus, irroratus, and albolhnbatus, seem to belong to one rather variable 



species " 



* In a specimen of Cricetodipus, I clearly see that a long slender spur is sent out from the squamosal, 

 like a clasp or hasp, lying above and reaching back of the meatus. Cf. what is said of an appar- 

 ently 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 eneroachmcut of the mastoid. 



3'2 M 



