SACCOMYIDJi— PEUOGNATillDIN^— PEB0GNATHU8. 



497 



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

 North American spejcies excepting P. fasc'uttux. They are so nearly similar 

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

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

 alities already presented. The description may be compared with that of 

 Dipodotnys given beyond. 



Although the temporal bone is largely developed in the mastoid element, 

 that lacks the enormous iiiHution seen in Dijtodomys, 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, anrf 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 Crke- 

 todipm, and is nothing at all like the regular clefl 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 the 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 Geomyidee, 

 though nearest the latter. T! " occipital is broader than in any other genus 

 of the family; the forks whic. mbrace the inter])arielal 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 ftom Mr. Alston's letter some passages wbioh bear opon the case, and show, farther- 

 uiore, with what oaation ninst not Dr. Oraji'H statemonts be received : — " The type of Ahromgt lordi is in 

 ba4 oouditioD, the ears being hopelessly distorted, but it seems to mo lo be DDdonbtodly P. monticola. 

 P. bicolor Qray, (from Honduras,) appears to I>e a good species, bat has been onriously badly drscribed. 

 It is daric lirown above, not blacic, and tho' the thr is sparse and somewhat bamh.itis not iu the least 

 bristly I Qray aeeins to have had both this specimen and bis Heltromni mtla»olt»eu» in his bands when 

 be wrote and to have confused one with the other. H. ie»mare»iianH$ Or. and B. adipenu* Ptn. will 



prove, I fancy, to be identical Dr. GUnther bas lately got a perfect spirit specimen of B. anoma- 



itu Tbomps., so we may expect a full aoconnt. of its anatomy. As yon surmised, Oray's fonr other 

 species, B, melaiiol«Heit$, longicaudatiu, imratui, and alboUmhalM, seem to belong to one rather variable 

 species. . . , ." 



* (n a specimen of CrioffodijiKt, I clearly see Ibat a long slender spur is sent ont 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 Dipodamf, beyond. It is, in this case, a slender 

 remnant of sqnamosal bone, left in an ordinarj- place, after most of the bone has been shoved into the 

 orbit by the uncruachmont of the mastoid. 

 32 M 



