PHYLOGENETIC ANALYSIS OF SOME SILURIAN ROSTROCONCHS (MOLLUSCA) FROM NORTHWESTERN CANADA

The new genus Avalanchia and the new species Avalanchia pterocarina, C assowarioides anisomorpha, Cassowarioides polgari, Nehedia bergeraci, Nehedia restricta, and Nehedia tricarina are proposed from exceptional ly preserved silicified faunas. Two new but unnamed rostroconch specie s are also described. These conocardioid rostroconchs were collected f rom Silurian deposits (late Llandovery to early Ludlow) near Avalanche Lake in the Mackenzie Mountains, Northwest Territories, Canada, and, when added to global rostroconch faunal lists, indicate a previously u nrecognized diversity of Silurian conocardioid rostroconchs. The morph ology of conocardioid rostroconchs is discussed, and a glossary of ter ms presented. Sexual dimorphism is recognized in species of Cassowario ides. Phylogenetic analysis of hippocardiids and bransoniids supports the monophyly of several genera. The hippocardiid genus Bigalea Pojeta acid Runnegar, 1976, is recognized as paraphyletic and three species are assigned to a new genus, Redstonia. Preliminary analysis of branso niids and hippocardiids for familial relationships, using data sets fr om the within-family analyses, indicates that the Bransoniidae is poly phyletic. The generic complex Mulceodens, considered to be derived bra nsoniid, is consistently reconstructed within a clade of derived hippo cardiids.