"Reithrodontomys megalotis caryi" A. H. Howell, 1935 (type locality, Medano Ranch, 15 mi. NE Mosca, Alamosa Co., Colorado), proposed for, and currently applied to, harvest mice from the San Luis Valley, Colorado, but possibly a synonym of aztecus according to Hooper (1952:218); and
"Reithrodontomys dychei nebrascensis" J. A. Allen, 1895 (type locality, Kennedy, Cherry Co., Nebraska), proposed for harvest mice from western Nebraska and adjacent areas, but regarded as a synonym of dychei by A. H. Howell (1914:30-31).
Our comments concerning the taxonomic status of these several names appear beyond.
We are grateful to Dr. W. Frank Blair, University of Texas, for the loan of a specimen from the Texas Panhandle (TU), and to Dr. Richard H. Manville, U.S. Fish and Wildlife Service, for the loan of specimens of R. m. caryi from the Biological Surveys Collection (USNM). We are grateful also to persons in charge of the following collections for allowing one of us (Jones) to examine Nebraskan specimens of R. megalotis in their care: University of Michigan Museum of Zoology (UMMZ); University of Nebraska State Museum (NSM); and U.S. National Museum (USNM). A research grant from the Society of the Sigma Xi facilitated travel to the institutions mentioned. Specimens not identified as to collection are in the Museum of Natural History of The University of Kansas. All measurements are in millimeters, and are of adults (as defined by Hooper, 1952:12) unless otherwise noted.
Secondary Sexual Variation
Hooper (1952) did not accord separate treatment to males and females in taxonomic accounts of Latin American harvest mice because (p. 11): "In no species ... does sexual dimorphism in the measurements, if present at all, appear to be sufficient to warrant separating the sexes in the analysis." Hooper did not statistically test the validity of treating the sexes together in R. megalotis. He did test a series of R. sumichrasti from El Salvador, in which he found no basis for separate treatment of males and females.
Some authors (Verts, 1960:6, for instance) have recorded females of R. megalotis as larger than males in external measurements, whereas others (Dalquest, 1948:325, for instance) have recorded males as the larger. In order to learn something of secondary sexual variation, and to decide whether or not to separate the sexes in our study, we compared adult males and females from the southern part of the Panhandle of Nebraska (Cheyenne, Keith, Kimball, Morrill and Scotts Bluff counties) in four external and twelve cranial measurements (see Table 1). The external measurements are those customarily taken by collectors and were read from the labels of the specimens; cranial measurements were taken to the nearest tenth of a millimeter by means of dial calipers, and are those described by Hooper (1952:9-11). Females from our sample averaged larger than males in all external and several cranial measurements, but individual variation greatly exceeded secondary sexual variation in each of these measurements and in no case was the greater size of females statistically significant. Therefore, and because we found no qualitative external or cranial differences between the sexes, males and females have been considered together in each population studied.
Table 1. Analysis of Secondary Sexual Variation in Adult Reithrodontomys megalotis From the Southern Part of the Nebraska Panhandle. For Each Measurement, the Number of Specimens Used, the Average, the Extremes, and One Standard Deviation Are Given.
| Character | Males | Females | ||||||
| Total length | 27 | 135.0 | (121-149) | ±6.14 | 32 | 141.0 | (127-149) | ±5.36 |
| Length of tail-vertebrae | 27 | 63.9 | (56-74) | ±4.63 | 32 | 65.2 | (58-73) | ±4.06 |
| Length of hind foot | 27 | 17.0 | (16-18) | ±0.60 | 32 | 17.3 | (15-19) | ±0.81 |
| Length of ear from notch | 27 | 12.9 | (12-14) | ±0.55 | 32 | 13.0 | (12-14) | ±0.61 |
| Greatest length of skull | 27 | 21.0 | (20.2-21.8) | ±0.43 | 28 | 21.3 | (20.4-22.2) | ±0.48 |
| Zygomatic breadth | 25 | 10.7 | (10.3-11.0) | ±0.21 | 28 | 10.9 | (10.4-11.3) | ±0.25 |
| Breadth of braincase | 27 | 10.0 | (9.6-10.5) | ±0.22 | 28 | 10.1 | (9.8-10.7) | ±0.18 |
| Depth of cranium | 26 | 7.9 | (7.4-8.4) | ±0.20 | 28 | 7.9 | (7.7-8.3) | ±0.15 |
| Length of rostrum | 27 | 7.3 | (6.8-7.6) | ±0.21 | 28 | 7.4 | (6.9-8.0) | ±0.27 |
| Breadth of rostrum | 27 | 3.8 | (3.6-4.1) | ±0.11 | 28 | 3.8 | (3.5-4.0) | ±0.12 |
| Length of incisive foramen | 27 | 4.4 | (4.1-4.6) | ±0.10 | 28 | 4.5 | (4.1-4.9) | ±0.19 |
| Length of palate | 26 | 3.5 | (3.1-3.8) | ±0.18 | 28 | 3.5 | (3.2-4.0) | ±0.15 |
| Alveolar length of maxillary tooth-row | 27 | 3.4 | (3.2-3.7) | ±0.14 | 28 | 3.4 | (3.2-3.7) | ±0.13 |
| Interorbital breadth | 27 | 3.1 | (2.9-3.3) | ±0.12 | 28 | 3.1 | (2.8-3.3) | ±0.11 |
| Breadth of zygomatic plate | 27 | 1.9 | (1.8-2.1) | ±0.10 | 28 | 2.0 | (1.9-2.3) | ±0.12 |
| Breadth of mesopterygoid fossa | 26 | 0.9 | (0.6-1.1) | ±0.12 | 28 | 0.9 | (0.8-1.2) | ±0.12 |
Pelage and Molt