Speciation and Evolution of the Pygmy Mice, Genus Baiomys

by Robert L. Packard

[9] Univ. Michigan, Museum of Zoology.

Baiomys musculus handleyi Packard

Baiomys musculus handleyi Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:399, December 19, 1958.

Baiomys musculus musculus, Goodwin, Bull. Amer. Mus. Nat. Hist., 68(1):39-40, December 12, 1934 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part).

Baiomys musculus nigrescens, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

Type.—Adult female, skin and skull; No. 275604 U. S. Nat. Mus. (Biol. Surv. Coll.); Sacapulas, El Quiche, Guatemala; obtained on April 24, 1947, by Charles O. Handley, Jr., original number 991.

Range.—Known only from the type locality in the valley of the Río Negro. Zonal range: Part of the Chimaltenangan Province of Smith (1949:235).

Diagnosis.—Size medium to large for the species; dorsum Wood Brown in some series to Buffy Brown; guard hairs of dorsum black-tipped, color of underhairs Avellaneous; hairs white to base in region of chin, throat, and median venter; in lateral region, hairs Neutral Gray at base; dorsal surfaces of forefeet and hind feet and ankles white; tail white below, brownish above; nasals truncate anteriorly; frontoparietal suture forming an obtuse angle with the suture separating the parietals; alveolar length of upper molar tooth-row and tail long. Average and extreme external and cranial measurements for nine adults from the type locality are as follows: Total length, 121.4 (115-128); length of tail vertebrae, 50.7 (49-54); length of body, 70.8 (66-77); length of hind foot, 15.3 (15-16); occipitonasal length, 19.6 (18.8-20.7); zygomatic breadth, 10.5 (10.2-11.0); postpalatal length, 6.9 (6.4-7.4); least interorbital breadth, 4.0 (3.9-4.0); length of incisive foramina, 4.2 (4.0-4.5); length of rostrum, 7.2 (7.0-7.7); breadth of braincase, 9.8 (9.7-10.2); depth of cranium, 7.1 (6.8-7.2); alveolar length of maxillary tooth-row, 3.5 (3.4-3.6); for photographs of skull, see [Plate 1c], and [Plate 3c].

Comparisons.—From B. m. nigrescens, B. m. handleyi differs as follows: everywhere paler; forefeet and hind feet whitish instead of dusky to sooty; hairs of anterior part of face white instead of brown; tail bicolored instead of unicolored; anterior tips of nasals truncate rather than rounded; frontoparietal suture forming obtuse angle with suture separating parietals instead of forming right angle; tail and upper molar tooth-row longer.