Only a beginning can be made at present with the problem of zoning the North American Jurassic on the basis of its brachiopods, but it is hoped that this beginning will encourage more accurate observation of the American Mesozoic species than has been made in the past. It is hoped that one of the chief difficulties of understanding Mesozoic brachiopods will soon be removed through the introduction of exact generic denomination in place of the improper use of Rhynchonella for all Rhynchonellidae, and Terebratula for both Terebratulidae and Terebratellidae. Rhynchonella is a Russian, Upper Jurassic brachiopod, unknown in North America. Terebratula is a late Cenozoic brachiopod, unknown in the Mesozoic. Paleontologists dealing with American Mesozoic species should bear these facts in mind.

Brachiopods are important and worth protracted investigation because of two things at least: they are guide fossils, and they are superior indicators of the temperature factor in . . .

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