Linnaeus (1758:64) described the eastern North American chipmunks under
the name _Sciurus striatus_ and based his description on that of Catesby
(1743:75). The Asiatic chipmunk was first described, under the name
_Sciurus sibiricus_, by Laxmann (1769:69). Schreber (1785, 4:790)
separated the Asiatic and North American chipmunks into the Asiatic and
American varieties. Gmelin (1788:50) followed Schreber and, employing
trinomials, used the names _Sciurus striatus asiaticus_ and _S. s.
americanus_. Illiger (1811:83) proposed _Tamias_ as the generic name of
the chipmunk of eastern North America. Say (1823:45) described _Sciurus
quadrivittatus_, the first species of chipmunk known from western North
America.
Trouessart (1880:86-87) proposed _Eutamias_ as the subgeneric name to
include the western North American and Asiatic chipmunks.
Merriam (1897:189-190) raised _Eutamias_ to full generic rank. In so
doing he neither listed nor described any characters but wrote that "it
will be observed that the name _Eutamias_, proposed by Trouessart in
1880 as a subgenus of _Tamias_ is here adopted as a full genus. This is
because of the conviction that the superficial resemblance between the
two groups is accidental parallelism, in no way indicative of affinity.
In fact the two groups, if my notion of their relationship is correct,
had different ancestors, _Tamias_ being an offshoot of the
ground-squirrels of the subgenus _Ictidomys_ of Allen, and _Eutamias_
of the subgenus _Ammospermophilus_, Merriam."
Howell (1929:23) proposed _Neotamias_ as the subgeneric name for the
chipmunks of western North America, of the genus _Eutamias_.
Ellerman (1940, 1:426) gave _Eutamias_ and _Neotamias_ equal subgeneric
rank with _Tamias_ under the genus _Tamias_; on pages 427-428 he quoted
Merriam, as I have done above, and later, after quoting the key to the
genera and subgenera of chipmunks of Howell (1929:11), Ellerman wrote
(_op. cit._: 428-429), "This key convinces me that all these forms
must be referred to one genus only. The characters given to separate
'_Eutamias_' from _Tamias_ are based only on the absence or presence of
the functionless premolar, and on the colour pattern. If colour pattern
is to be used as a generic character, it seems _Citellus suslicus_ will
require a new name when compared with _C. citellus_, etc." And again,
"The Asiatic chipmunk is intermediate between typical _Tamias_ and the
small American forms in many characters." To substantiate this, Ellerman
(_loc. cit._) quotes Howell (_loc. cit._), in comparing the subgenera
_Eutamias_ and _Neotamias_, as follows: "'the ears [of subgenus
_Eutamias_] are broad, rounded, of medium height, much as in _Tamias_;
postorbital broad at base, tapering to a point, much as in _Tamias_;
interorbital constriction slight, as in _Tamias_; upper molariform tooth
rows slightly convergent posteriorly, as in _Tamias_.'" Ellerman (_loc.
cit._) again quotes Howell (_loc. cit._), "'_Eutamias_ of Asia resembles
_Tamias_ of North America and differs from American _Eutamias_ in a
number of characters, notably the shape of the anteorbital foramen,
the postorbital process, the breadth of the interorbital region, the
development of the lambdoidal crest, and the shape of the external ears.
On the other hand, American _Eutamias_ agrees with the Asiatic members
of the genus in the shape of the rostrum, the well-defined striations of
the upper incisors, the presence of the extra peg-like premolar, and in
the pattern of the dorsal stripes.'"
Bryant (1945:372) wrote, "I am convinced that Ellerman's interpretation
of the relationships of the chipmunks is correct." After commenting
that the presence or absence of P3, "is of significance only in
distinguishing between species of squirrels," Bryant adds that "The
other differences between the eastern and the western chipmunks do not
appear to be of sufficient phylogenetic importance to warrant the
retention of the two groups as genera."