Fic. 15.—@ maxillary; 5 mandibular teeth of Paciculus 
insolitus Cope, twice natural size. Figs. =d, Hesperomys 
i 
of Oregon. 
todon ; c, frontal region from above, nat. size; 6 
maxillary teeth, a nat. size. 
Origina 
, 
From the John Day beds 
in the Loup Fo 
formation of N 
Mexico ad Ne e 
braska (A. die f 
don Cope). A 
gon, and 0 
have been pee 
tan. It was intermediate in size between the recent wood 
and mice, 
PacicuLus Cope. ' 
This genus is probably one of the Muridæ, anda near ally: 
recent Sigmodon and Neotoma. It differs from these genera in hav- 
ing three external inflections of the enamel in the superior mola 
instead of two. It differs from Hesperomys as these two ger 
viz., in having deep enamel inflections instead of tubercles 
valleys. It is true that the deepening and narrowing 
valleys of the molars of Hesperomys would result after w 
a pattern like that of Neotoma. The same process in Buí 
would produce a pattern much the same as that of Paciculus, 
that genus is further characterized by the contraction of the 
orbital region and the production of a sagittal crest, which 
found in Paciculus. 
Two species of this genus are known to me, P. ins 
smaller (Fig. 15 æ 4), and P. lockingtonianus, a larger one, 
is about the size of the wood-rat. Both are from the Jo 
beds of Oregon. They demonstrate an early origin for the / 
type of Neotoma, as contemporaries of the first of the He: 
mys. (Fig. 15.) 
PLEUROLICUS Cope, 
The exclusively American family of the subterranean - 
or Saccomyidz, was well represented in Orego™ 
probably in other regions, eins the John Day, ak 
phers,” 
The Æ. loxodon was smaller, 
See Fig. 15. 
