_a._ _B. t. analogous_, [F] ad., 120265, USNM, Zamora, Michoacan. _b._ _B. t. ater_, [F] ad., 15056, UI, 1-1/2 mi. ENE Greaterville, Arizona. _c._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa. _d._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality. _e._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S Aguascalientes. _f._ _B. t. subater_, [F] ad., 44543, USNM, type locality. _g._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas. _h._ Photo. of captive [M] _B. t. taylori_, 25 mi. E Austin, Texas. x 1.] [Illustration: PLATE 3 Photographs of skulls in ventral view of _Baiomys_. x 2. _a._ _B. m. brunneus_, [F] ad., 10834, AMNH, Jalapa, Veracruz. _b._ _B. m. grisescens_, [F] ad., 257080, USNM, Comayabuela, Honduras. _c._ _B. m. handleyi_, [F] ad., 275597, USNM, Sacapulas, Guatemala. _d._ _B. m. infernatis_, [F] ad., 91499, MZUM, Teotitlan, Oaxaca. _e._ _B. m. musculus_, [F] ad., 45462, USNM, Colima, Colima. _f._ _B. m. nigrescens_, [M] ad., 76834, USNM, Comitan, Chiapas. _g._ _B. m. pallidus_, [F] ad., 4802, Texas A & M, Axochiapan, Morelos. _h._ _B. m. pullus_, [F] ad., 71608, KU, 8 mi. S Condega, Nicaragua.] [Illustration: PLATE 4 Photographs of skulls in ventral view of _Baiomys_. x 2. _a._ _B. t. allex_, [F] ad., 45453, USNM, Colima, Colima. _b._ _B. t. analogous_, [F] ad., 120265, USNM, Zamora, Michoacan. _c._ _B. t. ater_, [F] ad., 15056, UI, 1 mi. ENE Greaterville, Arizona. _d._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa _e._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality. _f._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S Aguascalientes. _g._ _B. t. subater_, [F] ad., 44543, USNM, type locality. _h._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas.] _Remarks._--This subspecies retains its chief diagnostic character, blackish mid-dorsal region, throughout nearly all parts of its range. Specimens from the general area of Matagorda Bay and Lavaca County grade into _taylori_ in characters of color and crania. The Colorado and Brazos rivers seemingly serve as barriers reducing gene flow between _taylori_ and _subater_. These rivers may well have been important factors in the origin and the limitation of these two seemingly closely-related subspecies. _Baiomys taylori subater_ is not differentiated in color of pelage and characters of crania from _B. t. taylori_ to the same degree that _B. t. paulus_ is differentiated from _B. t. analogous_, or that _B. t. taylori_ is differentiated from several of the other subspecies of _Baiomys taylori_. _B. t. subater_ probably is a more recent occupant of the area in which it now lives than is the case with any other one of the subspecies of _taylori_. Sufficient time probably has not elapsed to allow for formation of more distinctive phenotypic patterns.