STRUCTURE AND AFFINITIES OF PROTOSTIGMARIA EGGERTIANA

Investigation of new, more or less complete specimens of Protostigmaria eggertiana reveals that it is a large, multilobed rooting structure produced at the base of a small arborescent lycopod. The trunk bears scars marking the point of attachment of leaves, and can be compared to the stem of Lepidodendropsis. In the largest specimens the root-bearing base is divided into about 13 lobes. In smaller, presumably younger specimens, fewer lobes are present. The roots are arranged on the lobes in series and orthostichies comparable to those of Isoetes. New observations on fiveand six-lobed Isoetes plants reveal a closer correspondence between Protostigmaria and Isoetes than previously recognized, and support suspected homologies among many fossil and extant lycopsid rooting structures. THE GENUS Protostigmaria Jennings (1975) was proposed for lobed lycopod rooting structures from the Lower Mississippian Price Formation of southwestern Virginia. As originally described, the underground system consists of three or more short lobes, each of which bears numerous rootlets that are comparable to the lateral appendages of Stigmaria, which in turn are comparable to the roots of Isoetes (Stewart, 1947; Frankenberg and Eggert, 1969; Karrfalt, 1980). For the purpose of this description, the lateral appendages of Stigmaria and the rootlets of Protostigmaria will both be termed roots because of their evident homology with the roots of Isoetes. Protostigmarian specimens are further characterized by circular or elliptical scars on the lobes that mark the positions from which roots were detached. Aerial parts of the plant have not been reported previously. Reexamination of the type locality and investigations at new localities have yielded several additional specimens of Protostigmaria. These are lobed structures attached to the base of arborescent lycopsid stems, and are apparently preserved in their original growing position. The newly discovered material indicates that Protostigmaria grew larger and developed more lobes than originally suspected. I Received for publication 22 March 1982; revision accepted 13 May 1982. This study was supported in part by NSF Grants DEB7725366 and DEB80-10793. We thank Dr. T. N. Bhardwaja for providing material of the multilobed Isoetes from Rajasthan, Ms. K. E. Sartain and Dr. S. E. Scheckler for information regarding collecting localities, and Mr. H. M. Sullivan for permission to collect. MATERIAL AND OCCURRENCE-The Price Formation in southwestern Virginia consists of a basal member that is predominantly coarse sandstone and conglomerate, and an upper member that is dominated by siltstone and shale in which coal seams are present and which contain the plant fossils. Upright trunks with protostigmarian bases have been observed at four localities. Locality number one (the type locality of Protostigmaria) is a roadcut on the east side of the U.S. Route 460 near Coal Bank Hollow approximately 4.2 km north of Blacksburg, Va. (9,250 F.S.L., 12,750 F.E.L., New Port Quadrangle). Specimens of Protostigmaria at this locality occur in a dark gray shale immediately underlying several thin coal seams or carbonaceous streaks. There is more than one such zone at this site, and as indicated by Jennings (1975), the best preserved material is located at the north end of the roadcut near the stratigraphic base of the exposure. Here upright stems have been found in connection with protostigmarian bases. Locality two is located along Route 640 in the valley of Tract Fork near Pulaski, Virginia (16,500 F.E.L., 16,125 F.N.L., Pulaski Quadrangle). Locality three is the Hurd Mine (16,125 F.E.L., 21,250 F.N.L., Pulaski Quadrangle). Locality four is a cut along the Norfolk and Western Railroad on Price Mountain (750 F.E.L., 19,750 F.S.L., Radford Quadrangle). At all localities Protostigmaria is preserved as combination mold-cast, compressionimpression specimens. Shortening of the vertical dimensions of the specimens as a result of compaction of the enclosing matrix during