PERIASTRON RETICULATUM UNGER AND AEROCORTEX KENTUCKIENSIS,N. GEN. ET SP., FROM THE NEW ALBANY SHALE OF KENTUCKY

Segments of anatomically preserved axes of the Lower Mississippian genus, Periastron, are analyzed in detail, and new features of histology and the pattern of vascular bundles are described. The name P. perforatum is shown to be a synonym of P. reticulatum. Division and fusion of vascular bundles in the axis result in variation in both their number (5–10) and form (in transverse section, from circular to elongate). In none of the 13 specimens studied is there any evidence of traces to lateral appendages, providing, with other evidence, support for the position that Periastron represents the petiole of a large leaf. Aerocortex kentuckiensis, a new name, is established for two specimens that resemble Periastron but which differ from it in being characterized by 2–4 vascular bundles in contrast to the 5–10 (or 11?) of Periastron, and by having centrally, rather than peripherally, located secretory ducts. Aerocortex and Periastron might represent, respectively, proximal and distal regions of a petiole.