xcvi Kodentia. MAMMALIA. Eodentia. 
Seit/irodon cumiculoides, Waterh., is the typical 
species, round in Patagonia. Its lengtli is about six 
and a half inches, with tail three and a half inches. 
lieithrodon typicus, WaterJi , is from La Plata, and 
is about the same size. 
lieithrodon chinchilloides, Waterh., is smaller. 
From the Straits of Magellan. All of these were 
brought away by Mr. Darwin, while attached to 
the English exploring ship “Beagle." Dr. Cones has 
established a sub-genus for the latter, which he de- 
nominates Euneomys. 
OcuETODON. — Co lies. 
Animals of this genus have the general resem- 
blance to the true Mice, but have the characters of 
Jlesperoinys, excepting that the superior incisors are 
deeply grooved lengthwise; hence the name, ochetos, 
meaning canal. The tail is about as long as the 
head and body. The form is slender and mouse- 
like, and very small. 'I'he genus comprises some of 
the smallest mammals in America. 'I’hey have a 
close general resemblance to ungrowu House-mice. 
'I'he teeth distinguish them readily, the molars hav- 
ing a peculiar aspect on the enamel loop, which re- 
sembles the Greek letter sigma; hence the name 
applied to the group — the Sigmodont Murinm. 'I’he 
upper incisors are grooved in a peculiar manner, also. 
This feature is uniq\ie with the North American 
Marinm. 'I'liese grooves are longitudinal, and are 
so prominent that when the incisors are closed, a 
deep notch appears, giving four points, instead of 
two, 111)011 the face of the teeth. 'I'he under incisors 
are simple. A number of marked peculiarities are 
also seen in the skull of this genus. 
LITTLE HARVEST MOUSE [Ochetodon humilis. 
{And. and Bach.) Cones '). — Much like the common 
House-mouse, but smaller. Inhabits the South 
Atlantic States, Sonora, and west to Nebraska. 
First described by And. and Bach., in 1841. 
LONG-TAILED HARVEST MOUSE {0. longicauda, 
{Baird) Cones). — Habitat, California. 
MEXICAN HARVEST MOUSE [0. mexicanus, (DeS.) 
Cones ). — Larger than either the preceding. It is a 
Mexican species, but found as far north as Louisiana. 
Sub-Famii.y — ARMI COLINS. 
'I’he characters are seen in the normally rootless 
molars (except in Evotomys), prismatic forms and flat 
crowns, the periphery being serrate. 'I’he incisors 
are often broader than deep, 'i’he palate is highly 
arched. 'I’he fore teeth are lai’ge and broad in com- 
l>,irison with the compressed and small incisors of 
the Mnrinm. 'I’he molars, also, are strongly con- 
trasted, those of the present group being so much 
larger than t hose of the other. 
Evotomys. — Cones. 
'i’his is the same as Hypudieus of Baird. It is 
much like Arvicola proper, but has ears plainly visi- 
ble above the fur. 'I’he molars are each two-rooted, 
the middle lower molar like the last one. 'I’he species 
are few in number. 'I’he North American may be 
recognized at once by their prominent ears, and 
tawny red color. 
Evotomys rntilus. {Pall.) Cones . — Dr. Coues says 
of this species : “ We have great pleasure in adding 
this interesting animal to our Fauna, our only pre- 
viously-recorded form being the variety gapperi, and 
the Mus rntilus of Pallas being supposed to be con- 
fined to the north of Europe and Asia.” Its habitat 
is given as “circumpolar regions of both hemis^ 
pheres.” Specimens have been found in Massachu- 
setts,- where it is not rare. 
RED-BACKED MOUSE [E. rntilus gapperi, ( Vigi) 
Cones ). — 'I’his is a form that is but .little removed 
from the preceding. 'I’he habitat is the northern 
frontier of the United States. 
Arvicola. — LacepMe. 
'I’he molars are |-f, rootless, perennial and pris- 
matic ; the crowns divided into several closed islands 
of dentine by folds of the surrounding sheet of 
enamel, that meet from opposite sides and fuse 
along the medium line. 'I’he pelage is thick, soft, 
of ortlinary fur, interspersed on the back with longer 
bristly hairs. 'I’he North American species are ar- 
ranged in four groups, which are regarded as quite 
natural. 'I’he generic term is derived from anum, 
a field, and cola, expressing habitation. 
Sub-Genos — Myono.mes. — liaf. 
'I’he teeth are concerned in this subdivision very 
considerably. 'I'he ear is unrimmed in front. '.I.’he 
fore-claws are not longer than the hind ones; the 
tail about one third the head and body, or more. 
“'I’his section is especially characteristic of North 
America, not being, perhaps, exactly matched in 
Europe and Asia. It embraces the greatest number 
of jAinerican species of the genus, among them the 
most widely distributed one of all, and includes, 
likewise, the largest one of all, while none of them 
are so small as our species of Ghilotus, Pitymys or 
Evotomys.” 'I'he peculiarities of dentition, as well 
as other generic characters, are of that nature that 
more space is required than we can give to the sub- 
ject. We content ourselves, therefore, by making as 
valuable an abstract as our limits will allow. 
COMMON AMERICAN-MEADOVI MOUSE [Arvicola 
[My onomes) rip arias, Ord). — Along name fora small 
creature, but the specific one is appropriate, meaning 
a river-bank animal. A very large synonomy is at- 
tached to the great work of Drs. Coues and Allen, as 
aj)plied to this species, many species being absorbed 
in the present. Dr. Coues says, after a very lengthy 
treatise on the subject : “In 18.o7, many names, all 
doubtless supposed by their several proposers to in- 
dicate valid species, were either formally or virtually 
suppressed ; and a further reduction of eight is 
simply an advance, pari passu, with the increase of 
our knowledge on the subject. AUe trust we have 
proven the position we take, and that we have seen 
the last of nominal sj)ecies base<l upon the endless 
variations oi Arvicola riparius.” 'I’his IMouse seems 
to be common in every part of North America, be- 
tween the two oceans above Virginia. 
