REVIEWS. 303 



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 Cre- 

 taceous of Greenland, the whole serving to fix very definitely the hori- 

 zon 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 him- 

 self. F. H. Knowlton. 



On the Organization of the Fossil Plants of the Coal-measures. By W. 

 C. Williamson. Philosophical Transactions Royal Society, Lon- 

 don : vol. 184 (1893) B. pp. 1-38 ; pi. 1-9. 

 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 Lepid- 

 odendron. Incidentally, the so-called genera Halonia and Uloden- 

 dron 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. 



F. H. Knowlton. 



