Abstract

Faunules of the Ptychaspis subzone of the Franconian stage appear to be widespread in southeastern Idaho and eastern Utah, but have not previously been described. The trilobite coquina limestone furnishing this collection is from the St. Charles limestone, 250 ft. to 273 ft. above the top of the Worm Creek quartzite member, on the ridge N of Mink Creek, Idaho. Ten genera and 14 species of trilobites, 2 genera and species of gastropods, 3 genera of brachiopods, Hyolithes, sponge spicules, and cystoid fragments comprise the assemblage. The new species, Ptychaspis bullasa, Idahoia (Meeria) modesta, Saratogia fria, Bellaspis? oblonga, Taenicephalina globula, Anconochilus idahoensis, and the new genus Minkella americana, are described. In the population of the latter species probable male and female forms are indicated. The faunule is placed at or near the top of the Ptychaspis granulosa teilzone. The appearance of Taenicephalina, Bellaspis, Lunkella, a member of the Dokimocephalidae, and 2 species of Pseudagnostus occurring also in eastern Nevada shows the first interminglings of far western or extracratonic faunal elements with a characteristic shallow shelf assemblage, a phenomenon fully compatible with the geographic position of the collection.

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