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Show ~46 ~XPLORATION OF TH.E OA.RONS OF THE COLOHADO. giving compiled indications only of several others. Woodhouse described a new species in 1853. Various naturalists of the Pacific Railroad Surveys furnished field-notea of observation, but their determinations, to state a wellknown fact, were not upon their own authority. In fact, the literature of the whole subject, so far as original work in rletermination of species is concerned, focu~es only in two authors-Richarrlson, 1829, anrl Baird, 1857. No species of Tlwmomys having apparently been described before 1829, the history of the genus may be considered to begin at that date. The eminent author of the Fauna Borcali -Amcricana gave five species of "Geomys" and "Diplo toma.'' One of these is a true Geomys; the four remaining ones (douglasii, butbi~,orum, tatpoides, and umbTinus), to which a fifth (borealis) was subsequently nddcd, are all Thomomys. These accounts of Richardson's remained for many y(-'ars the principal, and, in some cases, the whole, source llf what has been written upon the dcterminatiotl of species; and they inclurle every form of the genus known up to this date (every subsequent name proposed having proven a synonym). I hardly know where to look for the parallel of this curious case. Two points strike one in reviewing Richardson's work: First, he had a wholly erroneous idea that there were two rlistinct ~cnera, "Geomys" and "Diplostoma," in one of which the pouches, opening mto the mouth, dangled naturally as sacks on each side, and in the other of which the pouches were as we know them to be. This raclicully wrong premise vitiated all his work, and led him to the length of describing one and the same species as "Gcomys douglasii" a ncl "Diplostoma bulbivorum.'' Sec~ndly, the minute descriptions consist mainly of the repetition, under varymg forms of expression, of generic characters, common, of course, to all the species. When sifted. of their generalities, there is very little left; though, fortunately, such was th1s author'f:l habitual accuracy, the residuum suffices whe~ coupled with the indicaticms of loculit.y, for the identification of all hi~ species. As already stated, there was little real change in the state of the case from 1829 to 1857 '. when Professor Baird reviewed the subject, with considerably more matcnal and much more other inlormation than Richarclson a~Jpears to have pos-essed. "Diplo toma" had meanwhile been cffectuall d1sposed of; but to this author is due the credit of havincr first net 11 ·d y · fi 0 · . o ua v 1 en-tt c wtth speCimens several of Richardson's species, which, thougi1 often OOUES ON GEOMYS AND TllOMOMYS. 247 re-appearing by name, remained names only, with copied or compiled accounts attached. Professor Baird's only compilation was in the case of Tlwmomys "talpoides," which he did not claim to recognize. He examined the Philadelphia types of "borealis" and "townsendii," which Dr. LeConte had already satisfactorily located. He referred •· Diplostoma bulbivorum '' to the Californian fi>rm, remarking upon its close affinity to 1~ "douglasii," and established the identity of "umbrinus" with the New Mexican form. He adopted as distinct species the T. 1·ufescens of Maximilian and T. fulvu:~ of Woodhouse, and added a new one, T. laticeps. His descriptions arc like those of Richardson's in their minuteness and accuracy, which leave no doubt of his meaning, and the continual recurrence of comparative expression favors recognition of the discriminations .made ; but, as in the former case, they include much repetition of generic characters. It is a significant fact, however, that in this article the author omits the admirable antithetical tables he usually gives, and throughout seems to have rather undertaken the identification and clcscription of the species currently recognized at the time, than a critical reviiSion of the subject. Alluding to his lack of adequate material, he frankly characterizes the article as "a very unsatisfi:wtory account.'' I have only to add to this, that, as is well known, the tendency at the time Professor Baird's article was written was to pu h :specific discriminations beyond a point now usual. U odcr such circumstances as this sketch of t he history of the genus shows to have existed, it would be singular if some combination of currentlyrecognized species were not required. The rccluction I find necessary, and propose to make, is after all not a violent ouc. Holding for the mo111cnt the three form8 I shall describe as geographical races to be species-and they would he so regarded by any one working upon u. moderate number of specimens- the following arc the only combinations required: BAlUD, 1857. COUES, 1875. 1. J'homomys lmlbivums .. } { 2. J'homomys latiorps . . • . . Pacific coast region ...•••......••. . .. . . . .• -.-. DULDIVOJWS- . 3. Thomomys do~tglaBttH .. 4. 1.'1wmomys 1borca.lis . •. } { 6. Tlwmomys t'lifcscons . . . N ortllorn Interior ....• .. . . . • •..... -.. -.• -.. --. TALPOIDES -- • · 6. Thom.omys " talpoidos ". 7. TltOmomys 1tmbrinus . . . } Soutlwrn Intor.w r o.m1 L ower Co .1 1· r1 orm·o ... . ..... {uMDRJNUS . --. 8. ThomomJIB f~tlvua . .•• •. |