Xll] PSEUDOBOKNIA 11 



we must look elsewhere for the vegetative members of the 

 plant which produced cones of the Gheirostrobus type. 



In 1902 Professor Nathorst^ instituted the generic name 

 Psevdobornia for plants of which imperfect examples had 

 previously been referred by Heer^ to Calamites under the name 

 C. radiatus. Heer's plants were obtained from Upper Devonian 

 rocks of Bear Island in the Arctic seas and additional specimens 

 were brought from the same locality by the Swedish Polar 

 Expedition of 1898. Pseudobornia possesses jointed stems 

 (fig. 117, D) bearing whorled and shortly stalked leaves, often 

 four in number, at each node. The leaves are palmately 

 branched with fine serrated edges (fig. 117, C). Certain 

 specimens, which are no doubt correctly described by Nathorst 

 as cones, are characterised by a thick axis bearing whorled 

 leaves with sporangia on their lower surfaces, but the material 

 is not sufficiently well preserved to render possible a recognition 

 of structural details. It has been suggested by Scott that 

 Pseudobornia may possibly be referable to the Sphenophyllales 

 and that the stem of Gheirostrobus " may have had something 

 in common with " Nathorst's genus*. The beds in which the 

 stems occur are of Upper Devonian age, while Gheirostrobus 

 was found in Lower Carboniferous rocks : this difference in 

 age is not, however, a serious objection to the validity of the 

 comparison. We cannot do more than express the view that 

 Pseudobornia, so far as can be ascertained without an exami- 

 nation of petrified material or of more perfect impressions of 

 strobili, exhibits vegetative features not inconsistent with the 

 morphological characters of the fertile shoots known as 

 Gheirostrobus. 



The institution of a special group-name for the reception of 

 Sphenophyllum is justified by the sum of its morphological 

 features, which do not sufficiently conform to those of any 

 existing group of Pteridophytes to warrant its inclusion in a 

 system of classification based on recent genera. In the case of 

 Gheirostrobus we are limited to the characters of the cone and 



1 Kathorst (02) p. 24. ^ Heer (71) p. 32, Pis. i— vi. 



3 Scott (07) p. 155. 



