EARLY DDEVONIAN ACANTHODIANS FROM NORTHERN CANADA

Two unusual new genera and species of acanthodian fishes are described from the Lower Devonian of the Mackenzie Mountains, Northwest Territo ries, Canada. Kathemacanthus rosulentus gen. et sp. nov. is a deep-bod ied species that lacks a dermal shoulder girdle, but has a pectoral 'c ollar' or 'necklace' of large spines and enlarged scales, positioned i n series with a large pectoral fin and spine inserted high on the anim al's flank. K. rosulentus is assigned to the new monotypic family Kath emacanthidae. This family and the Brochoadmonidae constitute the new s uborder Brochoadmonoidei, characterized by the high pectoral spine and numerous short intermediate spines. Cassidiceps vermiculatus gen. et sp. nov. is also relatively deep-bodied, and it has a heavily armoured , small head. Brochoadmones, Kathemacanthus and Cassidiceps all lack d ermal shoulder girdle elements. Together they support the hypothesis t hat a dermal shoulder girdle is not primitive either for Acanthodii or for Climatiiformes. In the Brochoadmonoidei a complete series of vent ral intermediate spines precedes the well-developed pelvic fin and spi ne. In Brochoadmones the pectoral spine is greatly reduced, inserted h igh on the flank, and lacks a fin. In Kathemacanthus an oblique row of lateral intermediate spines precedes the well-developed pectoral fin and spine, whilst an apparently separate series of ventral intermediat e spines precedes the pelvic fin and spine. These data support Miles' earlier view that the prepectoral spines of other acanthodians belong to the same series as pectoral spines.