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) ===============+========+========+=========+========+========== Number | | Length | Length | Length | Upper of adults | Total | of | of | of | molar averaged | length | body | tail | hind | length | | | | foot |(alveolar) ---------------+--------+--------+---------+--------+---------- | _Baiomys musculus handleyi_ | Sacapulas, El Quiché, Guatemala | 9 Av | 121.44 | 70.77 | 50.67 | 15.33 | 3.48 Max | 128.00 | 77.00 | 54.00 | 16.00 | 3.60 Min | 115.00 | 66.00 | 49.00 | 15.00 | 3.40 2xStand. error | 3.60 | 3.22 | 1.26 | .44 | .05 ---------------+--------+--------+---------+--------+---------- | _Baiomys musculus pullus_ | 8 mi. S Condega, Nicaragua | 17 Av | 117.29 | 70.42 | 47.18 | 15.47 | 3.13 Max | 121.00 | 74.00 | 50.00 | 17.00 | 3.20 Min | 111.00 | 66.00 | 44.00 | 14.00 | 3.00 2xStand. error | 1.27 | 1.51 | .75 | .35 | .03 ---------------+--------+--------+---------+--------+---------- | _Baiomys musculus grisescens_ | Comayaguela, Honduras | 7 Av | 103.71 | 59.00 | 44.71 | 14.57 | 3.31 Max | 118.00 | 68.00 | 50.00 | 15.00 | 3.40 Min | 97.00 | 51.00 | 42.00 | 13.00 | 3.20 2xStand. error | 5.50 | 4.16 | 2.40 | .78 | .06