Ixxxii Kodentia. MAMMA.LIA.. Rodentia. 
ceding. From Santa Fe marls. Neotoma magister, 
B(drd. — This living genus has an extinct species, 
named as above, found in the caves of Pennsylvania, 
at Harrisburg and Carlisle. It is based on a number 
of under jaws, which average somewhat larger than 
those of the existing species. Arncola [Isodelta) 
speothen, Cope. — This and several others mentioned 
below are extinct species found in the bone caves 
of Pennsylvania, at Port Kennedy. A. (Pitgmys) 
tetradelta, Cope; A. [Pitymys] didelta. Cope; A. 
inwluta,Cope ; A. sigmodus,Cope ; A. [Anaptogonia) 
hiatidens. Cope. 
Geomvid,®. Geomysiisulcatus. Marsh. — From the 
Pliocene of Camp 'I’horne Loup Fork, Northern Ne- 
braska. Colotaxis crislatus, Cope. — -An extinct genus 
from the “ 'I'ertiary of the Plains.” There are three 
molars, with plicate crowns, two connecting cusps, with 
crescentic section on the outside, each of which gives 
rise to two transverse crests, which are unconnected. 
Of these crests, the anterior and posterior are mar- 
ginal and less developed than the median pair. 'I'he 
intervals are deep, without cement. 
JIysxricomorpiia — HYSTR icioai. llystrix venustus, 
Leidy. — This is an extinct species from the Plio- 
cene of Dakota. Dr. Leidy says : “'J’hey apparently 
indicate a species of Porcupine, but in structure are 
unlike those of the recent American Porcu})ine 
{Erethizon dorsatus), and exhibit a more evident 
relationship with those of the Crested Porcupine 
{Histi'Lv cristata) of FiUrope.” Jt is well known that 
the latter is not found living in America; conse- 
quently, this discovery is interesting, as introducing 
for the first time an Old World form of this family 
into our Fauna. 
Erethizon cloacinum, Cope. — 'I'his is an e.xtinct 
species of the present genus of American. Porcupines, 
found in Port Kennedy caves, Penn. ; determined 
from teeth, which exhibit a larger average size than 
those of the living species. In the I’liocene and 
Miocene of Europe, some forms of this family are 
found. 
Castoroididje. — This is an extinct family allied to 
Castor idee, and has a representative in Castoroides 
ohiensis. This “Fossil Beaver” was a most remark- 
able animal, its size being about that of a common 
JJlack Itear. A skull of this species measures over 
twelve inches in length, exceeding considerably that of 
the largest living Kodent — the Capybara. Certain an- 
atomical features of the skull indicate that the habits 
of tiiis animal differed greatly from the modern Beaver. 
'I'he discovery of portions of a jaw and teeth at Nash- 
j)ort, Ohio, and described by Dr. Foster, first brought 
the animal into notice. Dr. Wyman afterwards found 
the lamus of a lower jaw in Memphis, 'renn., and 
J)r. Leidy other fragments in South Carolina and in 
Illinois. Mr. Boll, of the Cambridge Museum, found 
some I'emains in 'Texas, in the alluvial deposits on 
'I’rinity Biver, associated with remains of the e.xtinct 
Horse and the Mastodon. “'I'he skull of this animal 
resembles the Castor, or Beaver, but the cranial i)or- 
tion is relatively very much smaller and more flat- 
tened, and the facial })ortion much larger than in 
tliat genus. 'The zygomatic processes arise at a 
much higher point, and the zygomatic arch is much 
less curved downwards. In Castor, on the contrary, . 
it reaches the small lachrymal, by which only it is 
separated from the anti-orbital process of the frontal. 
'The narrowest portion of the skull is behind the 
middle, instead of anterior to it, as in Castor. 'The 
basilar cavity seen in Castor is entirely wanting, and 
the auditory bullae are smaller. 'The molars differ 
strikingly in structure, not only from Castor, but 
from those of all other Rodents, except the Chin- 
chillidoR, a near resemblance being met with else- 
where only in the last molar of Hydrochaerus. 'They 
consist of a series of laminae of dentine completely 
inclosed by enamel, held together by a thin coating 
of cement. 'The circumference of the triturating 
surface of the tooth is thus devoid of the continuous 
plate of enamel that forms an uninterrupted border 
in the molar teeth of ordinary Rodents, and is deeply 
serrated. 'The molar teeth are essentially different 
from those of Castor, with which genus this form is 
usually compared.” Many other points of difference 
are recorded, which, with the above, are found in Prof. 
Hayden's Report on ifuriewtfa, before alluded to. 'The 
report also continues: “It will be seen that Cas- 
toroides presents a singular combination of charac- 
ters, allying it on the one hand to the Beaver, and 
on the other to the Chinchillas and Viscachas, and 
also to the Musk-rat, but which, at the same time, 
separate it widely from either group.” In si^ 
Castoroides exceeded any living Rodent, and is 
itself exceeded in this order by oidy a single extinct 
form of Hydrochoerus, described by Lund, from the 
bone caves of Brazil. From the wide differences 
noticed between this and its well-known allies, it is 
placed by itself as a type of a distinct and hitherto 
unrecognized family. 'The genera Amblyrhiza and 
Loxomylus, described by Prof. Cope, from the bone 
caves of Anguilla Island, West Indies, are referred to 
this group. 'The former has one species — A. inun- 
data, Cope ; the latter two — L. longidens. Cope, and 
L. latidens. Cope. 
Uydroci-kerid^. Hydrochoerus cesopi, Leidy . — 
In the Post Pliocene of the Ashley River, at Charles- 
ton, y. C., were found teeth referred to this genus, 
which includes the largest living Rodent — the South 
American River Hog [H. capyhara). 'These teeth 
differ from the existing form, and Dr. Leidy has es- 
tablished the above species. In the Brazilian Caves 
this family is represented, associated with Coelogenys, 
Dasyprocta and Kerodon. 'The last named is abun- 
dant in the Pliocene of La Plata. Cavia and Dasy- 
procta are found in the Miocene of Switzerland and 
France. No well-marked extinct genus of this 
family has been found. 
Lei>orid.e. — 'The Hares exhibit several extinct 
genera in the Miocene deposits of Dakota and Color- 
ado. Like the preceding forms, they are represented 
by only a few fragments of jaws and teeth, and none 
were of any considerable size over the ordinary 
living species. 
Paloiolagus haydeni, Leidy. — 'This was formerly 
called 'Tricium by Cope, several hundred specimens 
having been examined by the latter naturalist. A 
