VIII.—On the Schizochroal Eyes of Three Species of Reedops (Trilobita: Phacopidae) from the Lower Devonian of Bohemia

Abstract

Synopsis Bohemian specimens of the phacopacean trilobites Reedops cephalotes (Hawle and Corda,) R. sternbergi (Hawle and Corda) and R. bronni (Barrande) have very well preserved schizochroal eyes. The sizes and distribution patterns of the eye lenses were studied and in R. sternbergi and R. bronni the angular bearings of all the lenses were measured, giving the visual range of the whole eye. The internal anatomy of the eyes was also investigated, mainly from cut and polished sections. In many respects their morphology was comparable with that described previously in the Silurian and Devonian phacopaceans Phacops latifrons (Bronn) and Ananaspis communis (Barrande). The intralensar structures, however, are unlike those of P. latifrons and A. communis but bear a strong resemblance to the intralensar bowls of the Ordovician Zeliszkellinae, an early group believed to have been ancestral both to dalmanitaccan and post-Ordovician phacopacean stocks. A brief history of the evolution of schizochroal eyes is given, some distinctive evolutionary trends are noted and the relationship of the structural pattern in Reedops is discussed with reference to that in other Phacopina.