The Present Position of Palaeozoic Botany. 255 



at least to Psilotales. with which, on other grounds an affinitj- is 

 probable. The whole question of the systematic relations of the 

 Sphenophjdlales will be discussed below, at the close of the Section 

 on Lj'copsida; in the mean time it may be pointed out that they 

 clearly represent a synthetic group, combining the characters of 

 various other phyla, while at the same time showing distinctive 

 features of their own. We are thus led to suppose that the Spheno- 

 phyllales may probably have been the last, specialized descendants 

 of a very ancient common stock which, in all probability, reached it's 

 maximum at a time long prior to the Carboniferous, from which most 

 of our fossil evidence is derived. It is therefore extremely interesting 

 to find that Nathorst has recently demonstrated the existence in 

 Devonian times, of a striking type of plant, previously unrecognised, 

 which appears to have been at least related to the Sphenophyllales, 

 even if not referable to the same class. Fseudohornia ursina (Nathorst, 

 1894 & 1902) the fossil in question, from the Upper Devonian of 

 Bear Island, is at present only known in the form of impressions, 

 but the specimens are good, and the external characters well exhibited. 

 The main stems, which are believed to have been creeping, are 

 of considerable size, reaching about 10 cm in diameter in their 

 présent flattened condition. The stem was articulated and branched, 

 and on the smaller branches the whorled leaves are found in position. 

 Several are borne in a verticil, the number being most probably four, 

 according to Nathorst's careful observations; each leaf is of a 

 highly compound form; seated on a short petiole, it divides by 

 repeated dichotomy into several leaflets, which are themselves 

 deeply pinnatifid, with numerous fine segments. When the leaves 

 were first discovered, in an isolated state, they were supposed to re- 

 present some peculiar form of Fern- frond. The fructification is in 

 the form of long, lax spikes, bearing whorled sporophylls, resembling 

 reduced vegetative leaves. A sporangium appears to have been borne 

 on the lower part of the sporophyll, but there is no information as 

 to its mode of insertion. Indications of probable megaspores were 

 observed. 



This remarkable plant is provisionally regarded by its discoverer 

 as the type of a distinct class — the Pseudoborniales. As recognized by 

 Prof. Nathorst, there are certainly indications of affinity with the 

 Sphenophyllales and with the most ancient members of tlie Equisetales. 

 The complexity of the leaves suggests a comparison with Cheirostrobus, 

 which was characterized by so great an elaboration of the sporophjil, 

 but the Fseudohornia fructifications appear to have been widely 

 different. It is not improbable that the habit of the unknown stem 

 on which the Cheirosirohus strobili were borne may have had something 

 in common with that of Pseudobornia. In any case Prof. Nathorst's 



