Late Middle Cambrian Trilobites from Christmas Hills, Northwestern Tasmania

Two late Middle Cambrian faunas from Christmas Hills, northwestern Tasmania are of Lejopyge laevigata I or II Zone age. The previously undescribed trilobites from the lower fauna are described herein. New taxa described include Notacoosia plana gen. et sp. nov. and Mellacarella pulchella gen. et sp. nov. The morphogenesis of Nepea narinosa Whitehouse, 1939 is considered in detail. The fauna occurs within a buff-coloured, deeply weathered, laminated siltstone deposited below wave base. A quantitative analysis of over 1000 trilobite specimens reveals that the fauna is dominated by the agnostoid Tasagnostus debori Jago, 1976a, which comprises 53.8% of the total trilobite fauna and 79.8% of the agnostoids. Nepea narinosa comprises 62.6% of the polymerids and 20.4% of the total fauna. Although the percentage of the dominant species of agnostoid, Tasagnostus debori, is quite high, it falls within the range of species distribution of early Late Cambrian faunas from Canada.