| Abstract: | Three osteostracan genera, Tannuaspis, Tuvaspis and Ilemoraspis, from the Silurian and Devonian of the Autonomous Republic of Tuva and the Autonomous Region of Khakassia (USSR), are revised on the basis of the type material briefly described by Obruchev (1956, 1961, 1964). Tannuaspis bears some resemblances with the Tremataspididae. Tuvaspis may be closely related to Tannuaspis. Finally, there is no evidence of paired fins and cornual processes in Ilemoraspis (neither is there any evidence of their absence). Tannuaspis and Ilemoraspis share some characters which are not found in any other osteostracan: widely separated orbits, very small and oval lateral fields, situated at the same level as the median dorsal field. These resemblances may suggest that these two genera (to which Tuvaspis may be added) form a monophyletic group of osteostracans, which may be endemic to this part of Central Asia. |
