Comayaguela, Honduras), B. m. pullus differs in: dorsal ground-color and tail darker; sides and distal region of belly grayish instead of buffy-brown, thus making white stripe in region of belly distinct; average length of body and tail significantly longer, thus, total length greater; length of hind foot averaging longer (68 per cent confidence limits); alveolar length of upper molar tooth-row significantly shorter; occipitonasal and rostral length averaging longer; zygomatic spread and interorbital region narrower; length of incisive foramina, depth of cranium, postpalatal length, and breadth of braincase all averaging larger (see table 2).

From B. m. nigrescens (paratypes from Valley of Comitán), B. m. pullus differs in: dorsal ground-color slightly darker; facial region grayish, not sooty; mid-ventral white stripe present on belly and becoming grayish laterally; tail darker and less hairy, average length significantly longer; body, occipitonasal length of skull, incisive foramina, and postpalatal length averaging smaller; hind foot shorter; zygomatic spread, interorbital region and braincase broader (see table of measurements); cranium deeper.

Remarks.—B. m. pullus is the darkest dorsally of any subspecies of this species. Dalquest (1953:156) pointed out that preserved specimens of one of the subspecies of the northern pygmy mouse, Baiomys taylori taylori, tended to fade considerably over a period of four years. Post-mortem changes in color also are apparent in the southern species musculus. For example, the series of specimens from 8 mi. S of Condega, and 9 mi. NNW Esteli, Nicaragua, have faded from near Chaetura Black to the present Fuscous-Black in a period of two years. The most notable change in color came after the first six months of preservation. Allowing for this fading, the several color differences between pullus, nigrescens and grisescens are, nevertheless, distinctive.

Table 1.—Analysis of Variation in Adults of Four Subspecies of Baiomys Musculus (measurements in millimeters)