hylids have been derived from several phyletic lines. In each case the individual lines have undergone similar types of modifications in response to similar environmental situations. These frogs, which seemingly represent a reversal in the evolutionary trend in hylids, show several unique morphological characteristics by which they are functionally adapted to specialized modes of existence, first alluded to by Cope (1865:194) in reference to Triprion petasatiis: "It is interesting that an animal living in rocky situations should present such a cranial bony development; this, in connection with its colors, no doubt, aids especially in concealment, and is another instance of the Creator's bountiful care for his humblest creatures."
AcknowledgmentsThe completion of this study has been possible largely through the cooperation of museum curators and owners of private collections who have loaned, donated, or provided data for many valuable specimens. For their cooperation, I thank Mr.