fact, we think, that the published measurements of caryi average less than those given for R. m. aztecus by Howell (op. cit.:144) and herein. We have examined 16 of the 23 specimens from Medano Ranch and the single specimen from Del Norte that Howell listed. Unfortunately, none is fully adult. The specimens from Medano Ranch, collected in late October and early November, are mostly in fresh winter pelage or molting from subadult pelage, and closely resemble topotypes of aztecus in comparable pelages. Comparison of skulls of the specimens from Medano Ranch with skulls of topotypes and other individuals of aztecus of approximately equal age indicates that the Coloradan specimens may average slightly smaller and have somewhat shorter rostra. Externally, topotypes of caryi have the relatively long tail of aztecus and approach it in length of ear (measured on dry specimens). To us, they appear to be intergrades between aztecus and dychei, but to bear closer resemblance to the former, and we tentatively regard caryi as a synonym of aztecus. Benson (1935:140) noted that two adult topotypes of caryi were "similar to adult topotypes of aztecus." Specimens from southern Colorado east of the San Luis Valley, assigned to aztecus, are intergrades between it and dychei, as are two specimens from El Paso County, to the north, which resemble aztecus in color but resemble dychei in other characters and are tentatively assigned to the latter.

Specimens from southwestern Kansas and adjacent Oklahoma, herein referred to aztecus, also are intergrades with dychei. Individuals from Meade County, for example, are intermediate on the average between typical specimens of the two subspecies in color of upper parts (if anything, nearer dychei), resemble dychei in length of ear, but resemble aztecus in length of tail and rostral proportions (consequently also in length of skull). Although a case could be made for assignment of the specimens from Meade County (and elsewhere in southwestern Kansas) to dychei, they are, everything considered, nearer aztecus, to which subspecies they have been assigned consistently since first reported from the area by Hill and Hibbard (1943:24).

Of two specimens examined from 10 mi. S and 1 mi. W Gruver, Hansford Co., in the Panhandle of Texas, the one adult is clearly assignable to aztecus as is the specimen from 9 mi. E Stinnett, Hutchinson Co., Texas, that was referred to dychei by Blair (1954:249).

Reithrodontomys megalotis aztecus has had a rather unstable taxonomic history. Allen, who originally named the subspecies (1893:79), regarded it two years later (1895:125) as a synonym of R. m. megalotis, the subspecies with geographic range to the south and west of that occupied by aztecus. Howell (1914:30) recognized aztecus as valid, but he, too, questioned its distinctness from megalotis in a later paper (1935:144). Hooper (1952:218), the most recent reviewer, supported the validity of aztecus because specimens available to him averaged "distinctly larger in skull length and size of brain case" than specimens of megalotis. Our comparisons of typical specimens of aztecus with specimens of megalotis from southern New Mexico and southwestern Texas confirm Hooper's observations and indicate also that aztecus has a longer rostrum and slightly longer ear.

Reithrodontomys megalotis dychei J. A. Allen

Reithrodontomys dychei J. A. Allen, Bull. Amer. Mus. Nat. Hist., 7:120, May 21, 1895 (type locality, Lawrence, Douglas Co., Kansas).

Reithrodontomys megalotis dychei, A. H. Howell, N. Amer. Fauna, 36:30, June 5, 1914.

Reithrodontomys dychei nebrascensis J. A. Allen, Bull. Amer. Mus. Nat. Hist., 7:122, May 21, 1895 (type locality, Kennedy, Cherry Co., Nebraska).

Remarks.—From Reithrodontomys megalotis aztecus, geographically adjacent to the southwest, R. m. dychei differs as follows: upper parts averaging darker (especially in summer pelage), owing principally to more suffusion of blackish middorsally; tail slightly shorter; ears markedly shorter, rostrum shorter and relatively broader; occipitonasal length shorter owing to shorter rostrum.

"Reithrodontomys dychei nebrascensis," named by Allen (1895:122) from Kennedy, Nebraska, was distinguished in the original description from dychei by "slightly larger size, relatively longer ears, and more strongly fulvous coloration." Allen applied the name nebrascensis to harvest mice from Montana south to central Colorado and western Nebraska. Howell (1914:30-31) placed nebrascensis in synonymy under dychei because he found specimens from Kennedy to be "indistinguishable from specimens of typical dychei in comparable pelage." We concur with Howell. Topotypes of nebrascensis