Reithrodontomys megalotis caryi A. H. Howell, Jour. Mamm., 16:143, May 15, 1935 (type locality, Medano Ranch, 15 mi. NE Mosca, Alamosa Co., Colorado).
Distribution.—Western and southern Colorado, southeastern Utah, northeastern Arizona and northern New Mexico, east to the panhandles of Texas and Oklahoma and to southwestern Kansas.
External measurements.—Average and extremes of 10 adults (5 males, 5 females) from San Juan County, New Mexico, and adjacent Montezuma County, Colorado, are: total length, 140.1 (126-150); length of tail-vertebrae, 67.4 (56-71); length of hind foot, 17.3 (16-18); length of ear from notch, 15.1 (13-17); tail averaging 92.7 per cent of length of body. Corresponding measurements of 13 adults (7 males, 6 females) from Bernalillo and Guadalupe counties, New Mexico, are: 142.1 (129-156); 69.4 (60-75); 17.9 (17-19); 16.3 (15-18); tail averaging 95.4 per cent of length of body. Corresponding measurements of 22 adults (17 males, 5 females) from Meade County, southwestern Kansas, are: 147.1 (139-162); 71.3 (65-77); 17.6 (17-19); 13.8 (13-15); tail averaging 94.1 per cent of length of body. For cranial measurements see Table 2.
Remarks.—For comparisons with Reithrodontomys megalotis dychei, geographically adjacent to the northeast, see account of that subspecies.
When Howell (1935:143) named Reithrodontomys megalotis caryi from the San Luis Valley of Colorado he compared it directly only with R. m. megalotis from southern New Mexico and northern Chihuahua. Few adults were available to Howell from the San Luis Valley, accounting for the 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.
Specimens examined.—205, as follows:
Colorado. Alamosa County: Medano Ranch, 15 mi. NE Mosca, 16 (USNM). La Plata County: 1 mi. NW Florida, 6700 ft., 1; Florida, 6800 ft., 1. Las Animas County: 1 mi. S, 7 mi. E Trinidad, 2. Montezuma County: 1 mi. W Mancos, 5; north end, Mesa Verde Nat'l Park, 7000 ft., 3; Far View Ruins, Mesa Verde Nat'l Park, 7700 ft., 3; Park Point, Mesa Verde Nat'l Park, 8525 ft., 2; within 3 mi. Rock Springs, Mesa Verde Nat'l Park, 7500-8200 ft., 6. Prowers County: Lamar, 2. Rio Grande County: Del Norte, 1 (USNM).