Page:The Journal of geology (IA journalofgeology11893univ).pdf/319

ber, no less than eight are described as new to science. The new species belong to the genera Sequoia, Populus, Cissus, Alnites, Ficus, Diospyros, and Protophyllum. To these must be added four forms not specifically named, leaving sixteen species, having a distribution outside of the State of Minnesota. Of these sixteen species, fourteen are found in the Dakota group of Kansas and Nebraska, and six in the Cretaceous of Greenland, four species being common to the two localities. The species described as new, are more or less closely related to the forms from the Dakota group, or from the middle Cretaceous of Greenland, the whole serving to fix very definitely the horizon from which they came. The new, or especially interesting species are clearly depicted on the plates.

There are several obvious typographical errors as 'Kovne' for 'Kome,' 'nibrasciensis' for 'nebrascensis,' etc., which doubtless would not have occurred, had the author lived to read the proof himself.

This memoir, the nineteenth of this invaluable series, is devoted mainly to a consideration of the structure of Lepidodendron Harcourtii. This now classic plant was first named and described by Witham in 1833. It was also figured and described anew by Lindley and Hutton in their Fossil Flora of Great Britain, and was still later made the basis of an elaborate memoir by Adolph Brongniart. It was then referred by Brongniart to the cryptogams, but when he later discovered in allied forms, a secondary woody zone, developed exogenously outside of the central woody cylinder, he concluded that it must be a conifer. Williamson has long ago shown that the Lepidodendra frequently develop this secondary woody zone in mature stems, and that they are undoubted cryptogams. He was, however, unable to prove this for L. Harcourtii, for specimens well enough preserved to show internal structure, had not been before discovered. The present paper deals in an elaborate manner with all the authentic specimens, including the type of this species, and the author concludes that although none of the specimens were large enough to show the secondary thickening, this species is a true Lycopod, not unlike others of the genus Lepidodendron. Incidentally, the so-called genera Halonia and Ulodendron are treated of, the conclusion being that they are simply different forms of fruiting branches of Lepidodendroid and Sigillarian plants. This paper has a pronounced geological value, in that it affords a readily recognizable fossil, characteristic of a definite horizon.