. Biology of New World Microtus. Rodents; Rodents; Microtus; Voles. 130 Carleton spv. mpf-^ Fig. 3. Ventral view of two common palatal arrangements observed in Arvi- colidae: left, simple condition as exemplified by Clethrionomys gapperi, Virginia; right, complicated configuration as exhibited by Microtus pennsylvanicus, Wisconsin. For abbreviations, see Fig. 1. prevalence of such traits could be used to measure genetical differ- ences between local populations. In their pioneering studies of arvicolids, Hinton (1926) and Mil- ler (1896) attached particular taxonomic import to the bony archi-
. Biology of New World Microtus. Rodents; Rodents; Microtus; Voles. 130 Carleton spv. mpf-^ Fig. 3. Ventral view of two common palatal arrangements observed in Arvi- colidae: left, simple condition as exemplified by Clethrionomys gapperi, Virginia; right, complicated configuration as exhibited by Microtus pennsylvanicus, Wisconsin. For abbreviations, see Fig. 1. prevalence of such traits could be used to measure genetical differ- ences between local populations. In their pioneering studies of arvicolids, Hinton (1926) and Mil- ler (1896) attached particular taxonomic import to the bony archi- tecture of the posterior palatal region. Bailey (1900:10) gave palatal development as a trenchant generic character in his diagnosis of Microtus: "Palate with median ridge, distinct lateral pits, complete lateral bridges (not terminating in posterior shelf in any American species)." His description characterizes the more prevalent of the two basic anatomical plans recognized in Arvicolidae (Fig. 3). In the other, the palate terminates as a transverse shelf, with or with- out a median spine, and the palatal pits extend anteriorly and above the palatal shelf. This arrangement is seen in Clethrionomys, Eoth- enomys, and, to a lesser degree, in Lemmus. Although the palatal types seem clearly defined, assignment of genera, species, and some- times individuals to one condition or the other is sometimes equiv- ocal. Thus, Hooper and Hart (1962) stated that all degrees of intermediacy are found within Arvicolidae, and Rausch (1964) il- lustrated gradations between the extreme palatal configurations once thought to distinguish Old World M. gregalis from New World M. miurus. Hinton (1926:16) drew attention to the thick processes of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tamarin, Robert H; American
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