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Show 252 EXPLORATION OF TITE CARONS OF THE VOLORADO. border of Dakota-the details of external form checked from alcoholic specimens from Fort Bridger; in the latter respects, the account represent. nn amplification of the generic characters, and serves as a standard of comparison for the other species. in the account of which these full details need not be repeatcd).-So close is the general resemblance of this animal to Geomyt bursarius that, when the incisors are not examined, a second glance is requirc<l to distinguish them. The most obvious points of difference are the much smaller and weaker fore claws, altogether less mole-like (spade-lil<e) hands, and the decided though small external ears. 'rhe cheek-pouches are ampleif anything, more capacious than in Geomys bursarius or· tuza, and very decidedly larger than in other species of that genus. They extend fairly past (over) the shoulders to a point about opposite the elbow, when the fore limb is in a usual position. In comparison with pecics of its own genus, there arc, in 1~ talpoides, absolutely no decided points of difference in form. With vcrv " little modification in some detail , one description is equally applicable to them all, excepting T. clusius, in which there arc tangible distinctions. The general arrangement of the mouth-parts is as in Geomys bu'rsarius. Beneath the whisker-patch, on each side of the muzzle, about half-way from nose to eye, the fold of skin arises and curves loosely around, to subside again in the common integument over the posterior angle of the under jaw. In a fullgrown animal, the slit is an inch and a half long; the" slack'' of the edge of the pouch may be pushed an inch or more away from the cheek; the amplification of th~ sac .is here at a maximum-it reaches past the shoulder, as already said, and, m a full-grown animal, two fingers may be inserted to the second joint. The arrangement of the immediate mouth-parts is such that, as in Geomy~, the mouth appears io be a vertical fissure instead of a horizontal one, bounded on either side by thick, fleshy, and. hairy lips. This, however, is only the vc::;l i-bule of the mouth·' the buccal o1·1· fic,'e pr·o per be m· g sma 11 , c 1o sm· g hon·z untall v of course, as usual, remote from the upper incisors. which arc shut out corr;- pletel:.by u long, vaulted, hairy interval. The mucous membrane of the cheeks ~nly .iauly reaches the edge of the lips in a imall patch on either side, and 1ust 1.11 adva.n ce of the under incisors · Besides t·h e genera1 ha ·m ·n es of ' t h c b~ceal vcsttbule, there are longer and more hristly hairs, depending like a frmge around the roots of the incisors and marginin(J' the c.al l' r ' . ~ '' sc 1ps 10r some COUES ON GEOMYS AND THOJVJOMYS-'1'. TALPOIDES. 253 <listance.* 'rhe upper incisors are smoothly convex on their front face, with a very fine line of impression running immediately along their inner margin. This groove, always delicate and liable to be overlooked, is sometimes obsolete, or, nt any rate, fails to run the whole length of the tooth. The inferior inci~ or~ are similar, but longer, narrower, and with no sign of a groove. The l,lunt, tumid snout is entirely hairy, excepting a small .nasal pad, strictly con-· fined between the nostrils. The whiRkcr~ are very numerous, very fine and soft bristles (mostly colorless), and the longe t of them do not equal the head in length. A lew slight straggling bristles grow over the eyes and elsewhere about the head. The eyes are situated about midway between the nose and cars; they arc· small, only about an eighth of an inch in diameter, with rather t.umid lids. A notable peculiarity of the species of Thomomys, in compari on with Geomys, is the presence of external ears, about which there is no question. In Gfomys, the mere rim of integument warrants use of the terms "rudimentary" or "obsolete." In Thomomys, there is a very evident auricle, which rises behind, something lilw a quarter of an inch above the head; nor is it a mere rim even of this decided dimension; it tapers to quite a point uehind, and the lower border of the conch shows a slight folding, which represent's a rudimentary lobule. The cavity of the auricle admits the end of my pen-holder; the external meatus itself would admit a pigeon-quill. In the general shape of the body, there is nothing but what is shared by al~ the .,pccics of the family. The amplitude of the pouches is such that the width aero s them is much the greatc t diameter of the body. The next greatest girth is around the belly; the chest-measure is a little less than this. The fore and hind feet are as nearly as may be of the same length; either may slightly exceed the other, the difference being mainly due to varying development of the fore clawR. These, though decidedly fossorial (a familycharacter), arc not so enormously developed as in Geomy~ bursarius, being decidedly less than half the total length of the hund. The digits have the same relative lengtht'\, taken either with or without their claws: the 3d is longest, with the largest claw; the 2d is next; the 4th next, being about as much shorter than the 2d as this is less than the 3d; the 5th is abruptly much shorter, the tip of its claw scarcely or not reaching the ba"c of the 4th claw; the I :..;t i~": , horter , Lill, a mere stump, with u little knob for a claw. "No idoa wliatovo1· of tbe ti'UO configuration of tho mouLb·partl:l in this fumily can uo gai nou from dried sp::cimons from which tho slwll nnd leelh hnvo boon rcmovctl. |
