XXIl] NATHORSTIA 411 



Laccopteris is so close that generic identity might well be 

 assumed, but it has recently been shown by Nathorst^ that 

 the soral characters justify Heer's use of a distinctive name 

 for the Arctic fern. The circular sori arranged in two rows 

 (fig. 294, A, B) are superficially identical with those of Lac- 

 copteris, but consist of concrescent sporangia forming a circular 

 synangium (fig. 294, C, D) like those of Kaulfussia and 

 Ptychocarpus. The lighter areas in fig. 294, D, represent the 

 sporangia : fig. C shows the radial disposition of the numerous 

 sporangial compartments round a central receptacle. From a 

 stout midrib lateral veins arise at right angles, but their distal 

 terminations are not preserved. It is probable, as Nathorst 

 suggests, that Bayer's^ species Drynaria fascia from the Lower 

 Cretaceous rocks of Bohemia should be referred to Heer's genus. 

 In the absence of well-preserved sori it would be exceedingly 

 difficult, or even impossible, to distinguish between piimules of 

 Laccopteris and Nathorstia. 



A Tertiary species, Marattia Hookeri (fig. 261, C, p. 350), 

 described by Gardner and Ettingshausen' from the Eocene beds 

 of the Isle of Wight is referred by them to the Marattiaceae 

 because of a resemblance of the sterile pinnae to those of 

 M. Kaul/ussii ; but this is insufficient evidence of relationship. 



1 Nathorst (08). 



2 Bayer (99). ' Gardner and Ettingshausen (82) PI. xii. figs. 1—7. 



