A New Ordovician Graptolite from Oklahoma

Isolated graptolite specimens, obtained by dissolving lower Viola limestone (Middle Ordovician) in acid, represent a new genus and species, Orthoretiolites hami. Sicula, initial bud, and proximal part of first three thecae with continuous periderm, remainder of rhabdosome represented by clathria only. Thecae alternating, of orthograptid type, with straight ventral wall. Development of nonseptate diplograptid type. The new genus and species is distinct from Ordovician Retiolitidae and, despite reduction of the periderm, is placed in the Diplograptidae.