--------------+------------+-------------+-------------+-------------- INDIVIDUAL VARIATION Length of tail varied more than any other measurement used by me in taxonomic comparisons. Clark (1941:298), Hoffmeister (1951:16), and Van Gelder (1959:239) point out that external measurements generally are more variable than measurements of the cranium, probably because different techniques of measuring are employed by different collectors. As can be noted in table 3, females varied more than males. In the 3520 specimens examined, an extra tooth was observed in only one (see Hooper, 1955:298). The left mandibular tooth-row of an adult male (USNM 71539) from Omentepec, Guerrero, is worn more than the right one. Irregularities in number of teeth and abnormalities in individual teeth seem to be rare in pygmy mice. TABLE 3.--Individual Variation: Coefficients of Variation for Dimensions of External and Cranial Parts in a Population of B. Musculus and B. Taylori. =====================+=========================+========================= | Baiomys taylori | Baiomys musculus +-------------------------+------------------------- | Vic. (see page 595) | Vic. (see page 595) Measurement | Altamira, Tamaulipas | El Salvador +-----------+-------------+------------+------------ | 21 Males | 18 Females | 17 Males | 13 Females | C. V. | C. V. | C. V. | C. V. ---------------------+-----------+-------------+------------+------------ | | | | Total length | 3.0 | 4.7 | 4.9 | 3.7 Length of tail | 5.7 | 5.9 | 6.2 | 6.4 Length of body | 2.8 | 5.0 | 5.9 | 3.5 Length of hind foot | 3.7 | 3.4 | 3.0 | 4.1 Length of ear | 0.0 | 0.0 | 5.5 | 3.3 | | | | Occipitonasal length | 2.2 | 2.7 | 1.8 | 2.3 Zygomatic breadth | 3.6 | 3.3 | 2.2 | 2.7 Interorbital breadth | 3.2 | 3.3 | 2.2 | 2.9 Incisive foramina | | | | (length) | 3.8 | 4.6 | 2.5 | 3.2 Depth of cranium | 3.6 | 2.5 | 2.5 | 2.5 Alveolar length, | | | | upper molars | 2.7 | 2.5 | 2.8 | 3.2 Postpalatal length | 3.1 | 4.7 | 2.1 | 2.9 Length of rostrum | 3.3 | 3.6 | 2.4 | 4.7 Breadth of braincase | 2.7 | 1.4 | 4.0 | 4.9 ---------------------+-----------+-------------+------------+------------