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Determination of age of several species of vespertilionid bats by counting incremental lines in dentine, cementum, and peridontal bone is described. The technique was most effective for aging Eptesicus fuscus and Lasionycteris noctivagans and less so for Myotis lucifugus. Incremental lines in specimens of Lasiurus cinereus and Lasiurus borealis were clearly defined, while those in a Myotis californicus were not. Longevity of E. fuscus and longevity and apparent age structure of M. lucifugus agree with the findings of published banding studies.

Crania and bacula of five taxa of small-footed bats of the leibii group, comprising two currently recognised species, Myotis californicus and M. leibii, were studied to elucidate their interrelationships. Canonical variate analysis of 14 cranial measurements shows the existence of three distinct nonoverlapping clusters corresponding to (i) M. californicus, (ii) M. I. ciliolabrum and M. I. melanorhinus, and (iii) M. I. leibii. The results of the morphometric analyses do not support the claim that M. I. leibii and M. I. melanorhinus intergrade in Oklahoma. The taxonomic interpretation of the results is that the western forms of M. leibii represent a separate species M. ciliolabrum (Mcrriam). The bacula of the taxa studied lack distinctive characters that would allow one to discriminate between the species of the leibii group.