THE OTARIONINE TRILOBITE CYPHASPIS, WITH NEW SPECIES FROM THE SILURIAN OF NORTHWESTERN CANADA

The genus Cyphaspis Burmeister, 1843, is first known from the northern Laurentian Sheinwoodian. By the late Homerian, the genus had appeared in England and Baltica, and from the Ludlow through the Lower and Mid dle Devonian it had an essentially cosmopolitan distribution. The Miss issippian Dixiphopyge Brezinski, 1988, may represent a relict distribu tion of Cyphaspis, and if so should be considered a junior subjective synonym. Cyphaspis is considered the sister taxon of Otarion Zenker, 1 833. The oldest, Sheinwoodian, species of either genus are very simila r, but the clades evolved to the point of gross morphological disparit y in the Devonian. New species from the Wenlock and probably Ludlow of northwestern Canada are Cyphaspis lowei, C. munii, C. buchbergeri, an d C. mactavishi. New ontogenetic material of the Zlichovian C. dabrown i (Chatterton, 1971) further demonstrates the pervasiveness of the bas ic juvenile morphology of the tribe Otarionini.