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Spermatozoa in the Hyla rubra group (sensu lato) differ from those of all other Hyla species in possession of two tail filaments rather than one. Three distinct sperm-head shapes occur in the group, and a few species are somewhat intermediate or otherwise fail to precisely fit the categories. Comparison of sperm structure in Leptodactyloids prompts speculation of possible separate origins of certain Hyloid groups from Leptodactyloid stocks. Because anuran sperm structure appears conservative and differences seem to parallel those used as criteria in current classifications, sperm morphology provides a useful suite of taxonomic characters. Based on the diagnostic sperm-tail difference, plus pior definition of the Hyla rubra group, elevation of that group to generic status is judged valid, and is advocated. Ololygon is the oldest available name, and is tentatively applied, pending definite determination of the identity of the type-species, Hyla strigilata. At least five species-groups of Ololygon are tentatively identified. The 0. rubra group and 0. catharinae group are defined by sperm structure. Other species have a common sperm type; the 0. rostrata group is morphologically distinctive; other species are tentatively placed in the 0. staufferi and 0. x-signata groups. Additional species tentatively assigned to Ololygon are
Fouquette et al. (Mon,) studied this question.