CHEIROSTROBEAE 123 



At the same time, Cheirostrobus 1 combines in certain 

 respects the characters of Equisetales and Lycopods. 

 Thus the present genus throws great light on the 

 position of Sphenophyllum, which had previously been 

 quite undetermined. We can now scarcely doubt that 

 the Sphenophyllales generally were the highly modified 

 representatives of an ancient stock, with which both 

 Lycopods and Horsetails have affinities. 



PSEUDOBORNIALES 



5. Pseudobornia. — Professor Nathorst has recently 

 described a remarkable type of plant from the Upper 

 Devonian of Bear Island in the Arctic Ocean, which may 

 belong to the same stock with the Sphenophyllales. 

 Pseudobornia ursina 2 is only known at present in the 

 form of impressions, but the external characters are 

 shown in great perfection. The main stems, believed 

 to have been creeping, attain a diameter of about 

 10 cm. in their present flattened condition. The stem 

 was articulated and branched ; the smaller branches 

 still bear the whorled leaves, of which there appear to 

 have been four in a verticil. The leaves are compound, 

 dividing by repeated dichotomy into several leaflets, 

 each of which is deeply pinnatifid, with numerous fine 

 segments. The isolated leaves were formerly supposed 

 to belong to some unknown group of Ferns. The 

 fructification is in the form of long, lax spikes, bearing 



1 A fuller account of the organisation of Cheirostrobus is given in my 

 "Structure and Affinities of Fossil Plants from the Paleozoic Rocks," 

 Part i. On Cheirostrobus, Phil, Trans, vol. 189, B, 1897. 



2 A. G. Nathorst, " Zur Oberdevonischen Flora der Baren-Insel," Svenska 

 Vetmskaps-Akademiens Handlingar, Bd. 36, No. 3, Stockholm, 1902. 



