Eodentia. MAMMALIA. Rodentia. 
Ixxxi 
life six incisors are present. Tlie enamel of the in- 
cisors of this sub-order is present on both sides, but 
is considerably thinner behind. The skull has no true 
alisphenoid canal. The fibula articulates distal ly 
with the calcaneum. The testicles are externally 
situated. Two families only are known. 
Fossil Extinct Rodents. 
Members of this order are regarded as of very 
ancient lineage, some of the present living being- 
represented as far back as the Eocene. We are 
mostly indebted to the labors of Professors Marsh, 
Leidy and Cope for our knowledge of these forms. 
Among others who have discovered and described 
them may be named Prof. B. F. Mudge, of Kansas. 
SciURiDiE. — The bone caverns of Pennsylvania have 
yielded remains of extinct species of Tamias and 
Sciurus. The remains from the Tertiary deposits of 
the Western Territories, with one exception which 
is doubtful, are all of extinct genera. 'I’he genera 
Faramys and Sciuravus are abundant in the Eocene 
deposits. 'I’hese animals were, apparently, of size 
ranging from the Red Squirrel to those one fourth 
larger than the Woodchuck. Other forms are genera 
Taxymys, Marsh; Tillomys, Marsh; and Heliscomys, 
Cope. 
Sciurus calycinus, Cope, is an extinct species 
found in the Port Kennedy Bone Cave, Penn. About 
the size of the S. hudsonius. 
S. panolius, Cope, is from caves of Wythe County, 
Va. Smaller than the preceding by a third. 
S. relictus,Cope, is about the size of the Chickaree. 
From the 'I’ertiary of Colorado. 
'Tamias Iwvidens, Cope, is from the bone cave of 
Wythe County, Penn. 
Arctoniys vetus. Marsh . — This was about one 
third as large as the Arctomys monax, and is from 
the Loup Fork Pliocene, Nebraska. 
Paramys rolmstus. Marsh . — This was somewhat 
larger than the Woodchuck, and is from the Lower 
Tertiary deposits of Grizzly Buttes, Wyoming. 
P. leptodus. Cope, is about the same size, with 
smaller incisors. Locality, South Bitter Creek, Wy- 
oming. 
P. delicatus, Leidy . — About one fourth less than 
the former. From the Eocene beds near Fort Bridger, 
Utah. 
P. delicatior, Leidy . — Rather smaller than the 
preceding. Same locality. 
P. delicatissimus, Leidy . — Smaller than either the 
pi'eceding, and from same localities. 
Sciuravus nitidus. Marsh . — 'Phis is about the size 
of a Brown Rat. Grizzly Buttes, Wyoming. 
S. nudans. Marsh . — Rather larger than the pre- 
ceding. From same locality; and, by Prof. Cope, 
from Upper Green River, who refers it to Paramys. 
S. parvidens. Marsh . — Half the size of the last, 
with the teeth differing considerably. Henry’s Fork 
and Grizzly Buttes, Wyoming. Another species is 
described by Dr. Leidy, who regards it as somewhat 
doubtful as to the genus. 
Heliscomys vetus. Cope. — 'I’his genus is something 
like the Muridce; the species is smaller than S. hud- 
VOL. I.— L 
sonius, and is recorded by IMr. Allen as “ the smallest 
mammal of the Fauna to which it pertains.” From 
the 'I’ertiary of Colorado. 
Mysops fralermis, Leidy, is about the size of a 
Mouse, and is found in Grizzly Buttes, Wyoming. 
M. minutus, Leidy. — Size of the last. Wyoming-. 
Colonomys celer, Marsh. — About half the size of a 
Brown Rat. Henry’s Fork, Wyoming. 
'Taxymys lucaris. Marsh. — Rather smaller than the 
Flying Squirrel. From same place. 
Tillomys senex. Marsh. — About the size of a Rat. 
Same. 
T. parvus. Marsh, is a smaller species from Grizzly 
Buttes, Wyoming. 
'I’he Sciuridce are represented in Europe, in the 
Upper Miocene, by Spermophilus and Sciurus ; in the 
Newer Pliocene by Arctomys. In the Miocene of 
Europe, also, are Brachymys, Lithomys and Plesiarc- 
tomys; the • latter is intermediate between the 
Marmot and Squirrels. Wallace expresses the be- 
lief that the Squirrels are of an Old World type, and 
that they have entered the New World recently in’ 
a geological point of view. 
Castoridze. — Fossil remains of the Beaver have 
been found in New York and other States, associated 
with remains of Castoroides; they are found in the 
Post Pliocene and in the 'I'ertiary. 
Eucastor tortus, Leidy. — 'I'liis is an c.xtinct genus, 
found by Dr. Hayden on the banks of the Niobrara 
River; it was smaller than the Marmot or AVood- 
chuck. 
Steneojiher nehrascensis, Leidy . — 'Phis is another 
extinct form from the AVhite River, Dakota, on the 
Bad Lands ; it was about the size of the former. 
S. pansus. Cope . — 'Phis is a recent discovery from 
the Santa Fe .Marl Beds ; it is closely allied to the 
preceding. 
In Europe one species is found e.xtinct in the 
Upper Miocene. 'Progontheriuin is an extinct genus 
from the Post Pliocene of Europe, and anotlier — 
Chalicomys — is from the same. 
IsciiYRO.MiD.®. — 'Phis is an extinct family, named by 
Mr. E. R. Alston (Proc. Zolil. Soc., London, 1876), to 
receive Prof. Leidy’s genus Ischyroniys. 'Phe denti- 
tion is as in Sciuridce. 'Phe skull resembles Cas- 
toridoB, but with the infra-orbital opening large, a 
sagittal crest, no post-orbital process, palate broad, 
basi-occipital keeled. 
Ischyromys typus, Leidy. — About the size of a 
Musk-rat; the form of skull somewhat resembling 
that of the Beaver. From Bad Lands, Dakota. 
Gymnoptychus chrysodon, Cope.—¥ow species of 
this extinct genus are described by Prof. Cope. S. 
minutus is “scarcely larger than a House-mouse.” 
Pseudotomus Mans, Cope, is another form, about 
the size of the Agouti, having characters of Arcto- 
mys, Fiber, and some others. Locality, Bad Lands, 
Dakota. 
Myomorpiia — -MuridyE. Eumys elegans, Leidy . — 
In the Bad Lands of Bear Greek, Dakota, Dr. Hayden 
found a portion of the lower jaw, which indicates an 
animal the size of a Brown Rat, the genus being ex- 
tinct. E. coxodon. Cope. — A similar form to the pro- 
