Abstract

The stages Costonian—Onnian correspond roughly to the lower half of the Upper Ordovician as conceived in England. They embrace seven stages, the Costonian, Harnagian, Soudleyan, Longvillian, Marshbrookian, Actonian, and Onnian. These stages are subdivided into 32 zones, the zonal indices being chosen from the Dalmanellacea, Orthacea, and Strophomenacea. The brachiopod indices include 13 new species and varieties of which 4 are referred to Onniella, 5 to a new subgenus, 2 to a new genus, 2 to Wattsella and 1 to Dinorthis. An additional genus and subgenus and 3 new sub-zonal indices are also described. The indices referred to the 2 new subgenera and Onniella lie upon well-established trend-lines, their respective positions in the trends being defined by the statistical characters of the ribbing. The same method of definition is used in describing the other indices referred to Dalmanellacea.

PALEOZOIC SECTION IN VICINITY OF DOTSERO, COLORADO

BY CHARLES FERNANDO BASSETT* . . .

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