MURID—SIGMODONTES—HESPEROMYS LEUCOPUS. 75 
the specimens from Cape Saint Lucas in the nakedness of the tail and extension 
of the dusky on the metatarsus—the latter being one of the essential features 
of the species as compared with leucopus. In length of tail alone, these speci- 
mens grade into the ‘“‘gambeli” with which they are associated; yet, the 
other features being perfectly tangible and distinctive, we shall refer the 
specimens in question to aztecus, with no reasonable doubt of the correctness 
of so doing. 
As Mr. Xantus collected extensively on the west coast of Mexico, as well 
as in Lower California, it is possible that these examples of aztecus have been 
accidentally mixed with his Saint Lucas collections. 
The following table gives the measurements of a part of the specimens 
referable to leucopus (‘‘gambeli”) with measurements of some of them. 
Those representing aztecus will be found under the head of the latter. 
TaBLE XVII.—List of specimens of H. LEUCOPUS (“gambeli”) from Cape Saint Lucas, collected by J. Xantus, 
with measurements. 
Tail to end 
From tip of nose to— Length of— 
3 a | 
of— & 
i ; | Sa r) Nature of 
3 voce: Ocei Vv Fr Hind a specimen 
5 Eye. | Ear. aa Tail. es Hairs. f a f ~ = ; 
& put. ebra. oot. | foot.) = . 
4980 | Cape Saint Lucas..| 0.50 | 9.90 | 1.20 | 3.10 | 3.10 | 3.20 | 0.38 | 0.83 | 0.67 | Alcoholic. 
OBE | ssecece Giinpese sae 0.52 | 0.92 | 1.15 | 3.40 | 3.35 | 3.45 | 0.37 | 0.81 | 0.67 | Alcoholic. 
AQB2) |). s0-~ 00). --- = ----| 0.54 | 0.94 | 1.15 | 3.60 | 3.15 | 3.25 | 0.40 | 0.87 | 0. 70 | Alcoholic. 
10331 | | 
to Seni acee GS Apa ea tees sopeen saceao Sc6t 6||Saceec) |ao see] [seis seo||Soses||s=sccc | Alcoholic. 
| 10346 
Having exhausted the data at our disposal respecting the nominal species 
of Hesperomys (except ‘“cognatus”, noticed below) that are referable to 
leucopus, we are prepared to bring out three geographical races or varieties 
that are distinct enough, we think, in their strongest development at 
least, to merit varietal names, although (we wish it distinctly understood) 
they pass insensibly into ordinary /ewcopus. These three are gossypinus, 
sonoriensis, and eremicus. The first of these is nearest ewcopus, and is hard 
to define satisfactorily. The second is better marked, and, in its extreme, 
readily discriminated from /eucopus, though comparison of some hundreds of 
specimens show a perfect transition into the latter. The third is strongly 
marked as a local race, and might be held, with much show of reason, as a 
good species, as, in fact, we considered it until we saw intermediate specimens. 
