512 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 92 
Order PROBOSCIDEA 
STEGOMASTODON ARIZONAE Gidley 
Stegomastodon arizonae has for a type the greater part of a skeleton, 
No. 10707, including the basal portion of the skull with both tusks 
and the cheek teeth. To this were referred two other skeletal por- 
tions. One of these is of an older individual, No. 10556, and includes 
the basal portion of the skull with the cheek teeth and tusks, and the 
lower jaws as well as other portions of the skeleton. The third speci- 
men, No. 10917, includes only a portion of a hind limb and an associated 
lower jaw without teeth. 
Both Gidley (1926, pp. 86-91) and Osborn (1936, pp. 678-682) have 
given appreciable space to the description and discussion of this ma- 
terial. The form is clearly of the stegomastodont type and on the 
basis of the lower molars appears, as indicated by Gidley and Osborn, 
to be more progressive than the type of Stegomastodon mirificus. 
Osborn further notes that the third lower molar with seven and a 
fraction crests is also somewhat more progressive than that in Stego- 
mastodon texanus of the Blanco beds, but less progressive than the 
S. aftoniae type from Iowa. 
Order PERISSODACTYLA 
EQUUS sp. 
The Curtis ranch collection includes a number of isolated upper 
and lower cheek teeth, portions of jaws, foot bones and fragments of 
limb bones belonging to Equus. The form represented is not of great 
size, comparing favorably in this respect with material of Zquus semi- 
plicatus Cope from Texas or Equus lawrentius Hay from Hay Springs, 
Nebr. I hesitate to refer the Curtis ranch material to any one of 
the numerous species of Pleistocene horses because of the great need 
for revision in this group and also because I regard the stage repre- 
sented at Curtis ranch as somewhat earlier than the Pleistocene 
horizons represented at Rock Creek, Tex., and Hay Springs, Nebr. 
A few comparisons, however, are made with specimens representing 
certain of the forms which have been named. 
The upper molars compare favorably with the dimensions given 
by Cope ** for Z. semiplicatus, to which species the Curtis ranch 
material may belong, although the protocone in the Arizona teeth 
is not so elongate as in EZ. semiplicatus. The size of the protocone 
is noticeable in both Cope’s *7 and Gidley’s ** figures of the San Diego, 
Tex., skull referred by Gidley to &. semiplicatus. 
3°. D. Cope, 4th Ann. Rept. Geol. Surv. Texas, for 1892, p. 80, 1893. 
87. D. Cope, ibid, pl. 22, fig. 3. 
3 J. W. Gidley, Bull. Amer. Mus. Nat. Hist., vol. 14, pp. 129-130, fig. 21, 1901. 
