ANATOMY OF SIGILLARIA APPROXIMATA

Abstract

SINCE IT IS not always possible to correlate compressions and impressions with petrifactions, the names assigned to specimens showing external features only are often different from those given to petrified specimens of the same taxon. Sigillaria is one of the few genera in which the specific epithet given to a fragment with internal preservation has always been one which had previously been assigned to a compressed fossil with leaf bases similar to those in the petrifaction. Much can be said for and against such a practice. It is obviously a much more natural system of naming fossil plants and it avoids a multiplication of species names. In addition, since several of the species of Sigillaria are so similar as far as internal features are concerned, differentiating species on the basis of histological details alone would be impossible. A drawback of this system, however, would be encountered if stem fragments lacking leaf bases were found. Such a situation confronted the author in the present study of Sigillaria since none of the several woody axes available had cortex and leaf bases attached. Petrified Sigillaria stems are not especially common, and they are even rarer in North America than in Europe. In 1935, Graham described a crushed specimen of Sigillaria app,roximata Fontaine and White (1880), a clathrarian species of the genus, from a coal ball found in a coal mine near the town of Calhoun, in Richland County, Illinois. Darrah (1941) listed the same species from Iowa coal balls, but there is no description, nor does he cite a paper referring to its discovery in Iowa. Fisher and Noe (1939) indicated that S. elegans also occurs in Richland County, Illinois, but again there are no further details. MATERIALS.-Coal balls have recently become available in a creek bed about two and three-quarters miles east of Calhoun, Illinois, on the prpoerty of Mr. Lowell Steuber (NE 1/4 sec. 32, T3N, R 14 W, Sumner Quadrangle, Richland County). Coal was mined from the creek bed in the past, but operations have since been discontinued. The coal appears to be a continuation of the seam exposed in other nearby places (Graham, 1935; Schopf, 1941). Several coal balls from the recently discovered locality have yielded sigillarian remains in an excellent state of preservation. For reasons mentioned later in the paper, the species of Sigillaria present has been identified as S. approximata, and because of the quality of preservation of the material, a detailed study of the anatomy of that species could be made.