The Biostratigraphy of Glycymeris veatchii in California

Abstract

The stratigraphy and correlation of Upper Cretaceous rocks comprise one of the important problems of Pacific Coast geology, particularly as the search for petroleum extends to progressively older rock formations in California. This paper assists in the solution of the problem by tracing the variation and evolution of a single fossil molluscan species, Glycymeris veatchii, during Upper Cretaceous and early Tertiary time. Results of the present study are as follows: (1) the evolution of Glycymeris veatchii can be definitely traced; (2) the number of ribs on a valve in this molluscan group varies inversely with the geologic age of the specimen; and (3) two new varieties, Glycymeris veatchii reddingensis, and G. veatchii anae, and one new species, G. meganosensis, are recognized. The species G. major is shown to be invalid. A tentative correlation of the localities where Glycymeris is found in the Upper Cretaceous is presented. Systematic descriptions of species and varieties are included.