Among all the Paleozoic brachiopods no type of shell configuration has greater range, greater distribution, or greater representation than the rhynchonelliform shells, and previous to the appearance of the great work on the Genera of Paleozoic Brachiopoda, by Hall and Clarke,2 the more common custom was to refer all these shells to the genus Rhynckonella. It was pointed out by these authors, however, that the genotype of Rhynchonella, R. loxia Fischer, from the Upper Jurassic fauna of Russia, was, in its assemblage of external and internal characters, clearly distinct, generically, from any of our Paleozoic forms. They recognized, furthermore, no less than sixteen generic or subgeneric groups of rhynchonelliform shells in the Paleozoic faunas, to which either new names were given or for which previously published names were revived. No attempt was made by these authors to distribute all the species of Paleozoic Rhynchonelloids in their proper genera, but . . .