EECENT LITERATURE 
267 
is elevated to full specific rank, although it “agrees with microps in important 
features of the cranium” and the “two species are similar in their rather dark 
type of coloration, as well as in most other external features.” The differential 
characters mentioned are the larger size of levipes and details subject to consider- 
able variation. The author is usually careful and generally accurate in his de- 
scriptions, but the statement that the mastoid bullse in levipes are “fully twice the 
volume of those in microps” is inexact. This is a very variable character, as 
shown by the examination of paratypes of the two. The mastoid bullae of the 
larger examples of microps closely approach or about equal those of the 
smaller examples of levipes. Probably a study of the complete range of the levipes 
type of animal across Nevada to Utah and northward to Oregon would have led 
the author to adopt their original status as subspecies, not very strongly marked 
at best. 
The “Heermanni Group” is made to include four distinct species, Dipodomys 
panamintinus, D. leucogenys, D. mohavensis, and D. stephensi, with very limited, 
contiguous, or only slightly separated ranges in a region of general .physiographic 
conformity, mainly 'the desert basal slopes of the mountains in southeastern 
California. These all agree in the possession of a salient character indicating very 
close relationship, the decided expansion of the maxillary arches, which at once 
distinguishes them from externally similar species of the genus which frequently 
occur in the same localities. The forms mohavensis” and ^Heucogenys,” de- 
scribed as new species, vary considerably, but specimens from the type localities 
are slightly paler than topotypes of panamintinus and present slight cranial 
differences, mainly size, the kind of characters we learn by analogy to regard as 
of not more than subspecific value. Their combined ranges half encircle that of 
panamintinus, and other geographical considerations indicate the expediency of 
reducing them to subspecies, or reuniting all under a single name. In cranial 
details D. stephensi presents a rather slight departure from the panamintinus- 
leucogenys-mohavensis type in that the mastoid bullse are decidedly more inflated 
and there is a correlated reduction in width of the supraoccipital and interparietal, 
a condition not uncommon elsewhere in the genus. This form stands somewhat 
apart and should, perhaps for the present, be accorded specific rank, but as the 
characters are those usually found to be of subspecific value, intergradation may 
reasonably be expected. 
Two subspecies, D. nitratoides nitratoides and D.n. brevinasus are assigned to 
very limited ranges known to be broadly confluent in the bottom of the southern 
end of the San Joaquin Valley, an area presenting little diversity in faunal com- 
plexion. The characters pointed out are variable and these forms are not regarded 
by the reviewer as satisfactorily separable. Other cases might be mentioned, but 
these among the more extreme examples are indicative of the general method of 
treatment. 
While Doctor Grinnell may not be followed in all of his conclusions concerning 
speciation, the severest criticism being that this part of the work is over-done, 
he has succeeded admirably in the main purpose as announced by him at the 
outset ; but the degree of correlation between speciation and geography and envi- 
ronment can be satisfactorily ascertained without the recognition of an unwieldy 
number of forms. His elucidation of some complicated relationships will greatly 
facilitate the revision of the genus Dipodomys as a whole. 
— E. A. Goldman. 
JOURNAL OF MAMMALOGY, VOL. 3 , NO. 4 
