SACCOMYIDA—PEROGNATHIDIN A—PEROGNATHUS. 497 
an analysis of the species. I have before me 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 Diyodomys, 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 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 Geomyidea, 
though nearest the latter. The occipital is broader than in any other genus 
of the family; the forks which embrace the interparietal being fairly lamine, 
instead of mere linear spurs. The interparictal 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 case, and show, further- 
more, with what caution must not Dr. Gray’s statements be received : — “ The type of Abromys lordi is in 
bad condition, the ears being hopelessly distorted, but it seems to me to be 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, itis not in the least 
bristly! Gray seems to have had both this specimen and his Heteromys melanoleucus in his hands when 
he wrote and to have confused one with the other. H. desmarestianus Gr. and H. adspersus Ptrs. will 
prove, I funey, to be identical. .... Dr. Giinther has lately got a perfect spirit specimen of H. anoma- 
lus Thomps., so we may expect a full account of its anatomy. As you surmised, Gray’s four other 
species, H. melanoleucus, longicaudatus, irroratus, and albolimbatus, 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 sqnamosal bone, left in an ordinary place, after most of the bone has been shoved into the 
orbit by the encroachment of the mastoid. 
32 M 
