FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY—GAZIN 489 
this tooth is wider anteriorly but is so worn that any division of the 
anterior cusps has been obliterated. The last tooth in B. minimus 
is reduced to about the extent seen in B. taylori, not so much as in 
B. brachygnathus, 
PEROMYSCUS sp. 
A single right ramus, No. 10502, lacking the cheek teeth, but pos- 
sessing the incisor seems referable to Peromyscus. The tooth row 
as indicated by the alveoli is slightly longer than in the material 
of Peromyscus maniculatus gambelii examined, to which form Gid- 
ley compared the specimen, but is more nearly comparable, except 
for the slenderness of the incisor, to specimens of P. truez truei or 
P. eremicus anthonyi from the modern fauna of Arizona, 
BENSONOMYS, new genus 
Generic characters—Near Eligmodontia with knoblike process 
at anterior extremity of masseteric crest on lower jaw, last lower 
cheek tooth reduced, and sulcus between capsular and coronoid proc- 
esses. Removed from Hligmodontia in having deeper lower jaw, 
dorsally placed mental foramen closer to process at extremity of 
masseteric crest, more brachydont cheek teeth, notch on anterior 
lobe of first lower cheek tooth better developed, lower incisor more 
procumbent. 
Genotype.—Eligmodontia arizonae Gidley. 
BENSONOMYS ARIZONAE (Gidley) 
In addition to the type, which is a left lower jaw, No. 10503, with 
a complete dentition this species is represented in the Benson collec- 
tion by three other jaw portions that have preserved one, two and 
three cheek teeth, respectively. The incisor is present in each, ex- 
cept the jaw with one cheek tooth. 
In Gidley’s paper on the San Pedro Valley rodents the illustra- 
tions pertaining to “Hligmodontia” arizonae were unfortunately 
mixed with those of Onychomys bensoni, so that the citation, plate 
34, figure 15, preceding the text for “2.” arizonae, refers to a photo- 
graph of the type of O. bensoni that in no way conforms to the 
description given for “2.” arizonae. The type of Bensonomys arizonae 
is actually shown in plate 35, figure 3, captioned O. bensoni. The para- 
types of B. arizonae together with the description given for the type 
leave no doubt as to the true identity of type specimens. While the 
illustrations of the two type specimens involved are of little or no value 
in portraying the specific characters indicated in the text, they have 
in the past served to identify, erroneously, the specimens intended 
as the types, thereby confusing research and comparisons that have 
been made with these specimens. 
