PALAEOSTACHYA DIRCEI N. SP., AN AUTHIGENICALLY CEMENTED EQUISETALEAN STROBILUS FROM THE MIDDLE PENNSYLVANIAN OF SOUTHERN ILLINOIS

Palaeostachya dircei n. sp. is described from an authigenically cemented specimen collected from the Anna Shale Member occurring above the Herrin (No. 6) Coal Member and below the Brereton Limestone in the Carbondale Formation, Kewanee Group (Middle Pennsylvanian). The strobilus is three-dimensionally disposed within the matrix, allowing the preparation of ground thin sections, as well as selected maceration of the specimen. The imbricate strobilus is preserved for at least 7 cm of its original length and is composed of alternating whorls of sterile bracts and fertile sporangiophores. An articulated axis extends the length of the strobilus and attains a maximum width of 3 mm at the nodal areas. A whorl of 24 sterile bracts arises at each node, with each bract emerging at a 90? angle from the axis. Bracts are free except for a slight adaxial fusion at their point of origin. A slight downward-projecting keel develops at the point where the bract begins ascending at least past the second supra-adjacent node, where it is appressed into an abaxial furrow of the superposed bract. A whorl of sporangiophores originates above the bracts and is equal in number to the bracts. The sporangiophores are obliquely inserted on the axis and possess four superposed and thin-walled sporangia inserted upon a (?) cruciate head. Spores assigned to Calamospora have been recovered and range in diameter from 68-115 ,um (x = 89 ,um). The cone appears to be homosporous. Palaeostachya dircei n. sp. is compared to the reported permineralized and coalified compression species and appears similar to P. vera Seward and P. gracilis Renault. THE DELIMITATION of Carboniferous strobili of the Equisetaceae (sensu Good, 1975) is based primarily upon the relationship between the sporangiophore and the bract. Twelve genera of strobili, based upon coalified compressions and permineralizations, are recognized in the Carboniferous. Palaeostachya Weiss (1876) was erected for fructifications which possess an articulated axis with alternating whorls of bracts and sporangiophores, with the origin of the sporangiophore stalk at or slightly above the level of bract attachment, and obliquely inserted. Four sporangia are usually attached to the sporangiophore head and directed towards the cone axis, although three 1 Received for publication 12 August 1980; revision accepted 21 October 1980. Supported in part by a Sigma Xi Grant-in-aid of Research, an award by the Karl P. Schmidt Fund, Chicago Field Museum, and a Dissertation Research Award granted by Southern Illinois University, Carbondale. The author would like to thank Dr. Eugene Richardson, The Chicago Field Museum, Dr. Richard Leary, The Illinois State Museum, Springfield, Illinois, Dr. Francis M. Hueber, the United States National Museum of Natural History and Dr. Sergius Mamay, the United States Geological Survey for their assistance and support, and Dr. Lawrence C. Matten and Professor William C. Darrah for their critical review of the original manuscript submitted in partial fulfillment for a Ph.D. degree in the Department of Botany, Southern Illinois University, Carbondale. species have been described possessing two sporangia per sporangiophore head. Twenty species of Palaeostachya have been established, and a review of the taxa shows that some species are probably assignable to genera in which the bract: sporangiophore relationship is uncertain. An authigenically cemented Palaeostachya was collected from the Anna Shale Member above the Herrin (No. 6) Coal Member west of Carterville, Illinois (SE4 Herrin 15' Quadrangle, S4-T9S-R1E) and is curated in the Southern Illinois University Paleobotanical Collection (SIPC). The Anna Shale Member is placed within the Carbondale Formation, Kewanee Group (Hopkins and Simon, 1975) and is Middle Pennsylvanian in age (Westphalian D/? Cantabrian equivalent). Hibbert and Eggert (1965) have reported the only other equisetalean strobilus collected and described from the Carterville locality, Paracalamostachys cartervillei. Permineralized specimens of equisetalean strobili are easily delimited to a generic and specific level because serial thin sections are easily prepared utilizing the cellulose acetate peel technique (Delevoryas, 1955; Baxter, 1955; Taylor, 1967; Good, 1975). The relationship between the sporangiophore and bract as well as other anatomical and morphological