Ixxxiii 
Kodentia. MAMMALIA. Bodentia. 
detailed account of tlie peculiarities is found in 
Hayden’s Report, Hodentia, 1877, where also will be 
found the references to original descriptions. 
P. agapetillus, Cope, is smaller tlSin the preceding, 
with larger Incisors. A larger is P. turgidus. Cope, 
and another form is P. triplex, each from the same. 
Panolax mnctm-Jidei, Cope, is named from its lo- 
cality, Santa Fe. It was about the size of the com- 
mon Northern Hare. This genus is not clearly defined, 
according to the author, and is provisionally recorded. 
Praotkerium palatinuvi, Cope, is from the Port 
Kennedy Bone Cave, Chester, Penn. 
Fossil remains of existing species are found in the 
various bone caves of America, associated with other 
Mammalia. In the crevices of lead-bearing rocks of 
Illinois, and in the Post Pliocene deposits of Ashley 
River, in Charleston, S. C., they are found. Lepus 
braziliensis occurs in the caves of Brazil. Lepus 
occurs in the Post Pliocene of France. A gigan- 
tic animal, which has received the name Toxo- 
don, is considered to have close affinity with the 
Rodents. The species T. platensis had incisors like 
the Hare. Prof. Owen remarks: “The dentition 
closely resembled the Rodent type, but manifested it 
upon a gigantic scale, and tended to complete the 
chain of affinities which link the Pachydermatous 
with the Rodent and Cetaceous orders.” B’Orbigny 
has later determined, from a discovery of another 
species, the fore-arm being secured, that the creature 
had limbs not unlike the 'I'apir and Capybara ; to 
the latter it bears most resemblance. It is judged 
that its length must have been from twelve to six- 
teen feet. The skull was two feet four inches in 
length, and one foot four inches across Its breadth. 
The family Toxodontidce is formed to admit the two 
species. 'L'he remains were found in South America, 
near Bahia Blanca, by Mr. Darwin. 
The Bipodidm, an Old World family, is represented 
by extinct forms in the Miocene of the Alps and in 
France, the Myoxidce in the Maltese caverns, and in 
France and Switzerland. 
'l’he extinct group HebetidenUiti, nearly allied to 
the Rodents, has some peculiarities of dentition. 
'I'here are two incisors in the upper jaw, and four in 
the lower, the outer ones of the lower jaw very 
small, 'l’he enamel is continuous around the teeth ; 
the crowns are transversely hollowed, and the points 
chiseled. 'l’he fibula articulates with the calcaneum. 
One family only is recognized — the Mesotheriidm — 
of which one species is known, from the Pliocene of 
South America. 
Extinct ChinchillidcB are found in the caves of 
Brazil and in the Post Pliocene of La Plata. Species 
of the family Octodontidm are found in Pliocene 
of La Plata, 'i’he Eocene of South America pro- 
duces Megamys, an extinct genus, allied to Gapro- 
mys, both of this family. In Europe, the Lower 
-Miocene yields two extinct genera of the same — 
Palaeomys and Archmomys. 
'l’he iAmWgEchimyidce is represented in the Brazilian 
caves by an extinct species of the genus Garterodon. 
and the extinct genera Myopotamus, Loncheres, Lon- 
chophorus and Phyllomys. In the Upper Miocene of 
France there are numerous species of the extinct 
genus 'I’heridomys, allied to Cercolahidm. In the 
Upper Miocene of Germany is an extinct genus, 
Aulacodon. The Brazilian caves produce a large 
species of Gercolabes. 
Lagomyidoe. — Extinct forms of this family are seen in 
the Post Pliocene of Europe. In the Miocene of France 
and Germany is found the extinct genus 'rilanomys. 
Family— SGIURIDHC. 
The Squirrels are the typical forms of this family. 
'The dental formula is now stated as follows : Inci- 
sors, I ; Premolars, or j- j- ; -Molars, or 
|g. 'l’he molars are rooted, with tuberculated crowns 
during youth ; the tubercles soon become much 
modified, or nearly obliterated by attrition, giving 
the form of transverse ridges. 'l’he first upper pre- 
molar, when two are present, is often minute, and is 
generally much smaller than the second. 'l'he feet 
are either scansorial (fitted for climbing), or fos- 
sorial (suited to digging in the earth). Perfect clav- 
icles are present, and nearly perfectly free fibulae. 
'I’here is a small, naked muffle, and a cleft upper lip. 
'l’he Sciurines are found throughout all the conti- 
nental portions of the world, excepting Australia, 
but are notably more numerous in the northern 
hemisphere. 'l’he genus Sciurus is universally dis- 
tributed, with the above exception. Gynomys, on 
the other hand, is limited to a small portion of North 
America. Spermophiles are more numerous in the 
latter country. Pteromys occurs only in the tro- 
pical portions of Asia, and Xerus in Africa. In 
South America the Sciurines are represented only by 
the genus Sciurus, and by a few species only. 'I’hey 
are more abundant in Gentral America, and the 
genus Sciurus is found to have more species in 
Southern Me.xico than in any equal area in the New 
World. In the United States, not over three species 
are found in one locality together, and north of that, 
not over one is known. Europe has a single species; 
but they occur somewhat more abundantly in Asia 
and Africa. 'l’he forms under consideration have 
been the subject of minute investigation, and much 
confusion has of late been dispensed by the assidu- 
ous labors of our American naturalists. Since the 
year 18.50, the North American Sciuri have been 
reduced in numbers from twenty-seven species to si-x, 
with six or seven additional geographical races or 
sub-species. “ 'l’he species,” says Professor Baird, 
“exhibit an unusual tendency to run into varieties of 
color, among which gray, red and black are the pre- 
dominating ones, with all possible intermediate 
shades, 'these varieties are sometimes more or less 
constant in particular localities, sometimes changing 
with every litter.” 'I’his group of Rodents seems 
particularly to have a tendency to melanism, the op- 
posite ol albinism. 'I’here are jet black Squirrels, and 
occasionally pure white ones, with the pink eyes that 
are characteristic of this condition. 
SciUROPTERus. — F. Cuvier. 
'I’his genus is characterized most remarkalily by 
the extensive expansion of the skin between the fore 
