300 



DE. J. W. DAWSON ON" NEW 



The only species known to me is represented by a stem 2-5 cen- 

 timetres in diameter, slightly wrinkled and pitted externally, per- 

 haps by traces of aerial roots which have perished. The transverse 

 section shows in the centre fonr vertical plates of scalarit'orm or 

 imperfectly reticulated tissue, placed at right angles to each other, 

 and united in the middle of the stem (figs. 1-4). At a short distance 

 from the centre, each of these plates divides into two or three, so as to 

 form an axis of from ten to twelve radiating plates, with remains of 

 cellular tissue filling the angular interspaces (fig. 3, h). The greatest 

 diameter of this axis is about 1*5 centimetre. Exterior to the axis 

 the stem consists of elongated cells (fig. 7), with somewhat thick 

 walls, and more dense towards the circumference. The walls of these 

 cells present a curious reticulated appearance, apparently caused by 

 the cracking of the ligneous lining in consequence of contraction in 

 the process of carbonization. Imbedded in this outer cylinder are 

 about twelve vascular bundles (figs. 2, 3, d), each with a dumb-bell- 

 shaped bundle of scalariform vessels enclosed in a sheath of thick- 

 walled fibres. Each bundle is opposite to one of the rays of the 

 central axis. The specimen shows about two inches of the length of 

 the stem, and is somewhat bent, apparently by pressure, at one end. 



This stem is evidently that of a small tree-fern of a type, so far 

 as known to me, not heretofore described *, and constituting a very 

 complex and symmetrical form of the group of Palaeozoic Eerns 

 allied to the genus Zygopteris of Schimper. The central axis 

 alone has a curious resemblance to the peculiar stem described by 

 Unger (* Devonian Elora of Thuiingia') under the name of Cladoxylon 

 mirabile; and it is just possible that this latter stem may be the axis 

 of some allied plant. The large aerial roots of some modern tree- 

 ferns of the genus Angiopteris have, however, an analogous radiating 

 structure. 



The specimen is from the collection of Berlin TL Wright, Esq., 

 of Penn Yan, New York, and was found in the Portage group 

 (Upper Erian) of Milo, New York, where it was associated with 

 large petioles of ferns and trunks of Lepidodendra, probably L. 

 chemungense and L. primoevum. 



In previous communications to the Society I have described three 

 species of tree-ferns from the Upper and Lower Devonian of New 

 York and Ohio ; and this species is from an intermediate horizon. 

 All four occur in marine beds, and were, no doubt, drift-trunks from 

 the fern-clad islands of the Devonian sea. The occurrence of these 

 stems in marine beds has recently been illustrated by the observa- 

 tion of Prof. A. Agassiz, that considerable quantities of vegetable 

 matter can be dredged from great depths in the sea on the leeward 

 side of the Caribbean Islands. The occurrence of these trunks 

 further connects itself with the great abundance of large petioles 

 (Rhachiopteris) in the same beds, while the rarity of well-preserved 

 fronds is explained by the coarseness of the beds and also by the 

 probably long maceration of the plant-remains in the sea-water. 



* Prof. Williamson, to whom I have sent a tracing of the structure, agrees 

 with me that it is new. 



