16 ARKIV FÖR BOTANIK. BAND 17. N:0 1. 



time regarded as a subgenus of Polypodium. The idea of a 

 relationship in this direction has since been elaborated, espe- 

 cially by Seward. Professor Seward and IMiss Dale (1900, 

 1901) proposed the removal of Dipteris from the Polypodiaceae 

 to form a separate family and brought to this family several 

 Mesozoic genera, among them Dictyophyllum. It seems to 

 have been the general opinion since then, that Dictyophyllum 

 and other similar genera are actual members of the Dipteri- 

 dinae: Zbiller (1903, p. 97), for instance, says that Seward & 

 Dale's attribution of the genus to that family »semble ab- 

 solument justifiée». 



Nathorst, however, in his memoir on Dictyophyllum 

 and Camptopteris remarks on several important points of 

 difference between Dictyophyllum and Dipteris. He points 

 out especially that the sporangia of Dictyophyllum occur in 

 a smaller number in each sorus, are much larger and more 

 rounded than those of Dipteris, and apparently have a some- 

 what better develojied annulus. Nathorst does not express 

 any definite opinion as to whether Dictyophyllum should be 

 referred to the Dipteridinae in spite of these differences or 

 not, but he remarks that it might be a more cautious course 

 to place it provisionally in a separate sub-family for which 

 he proposes the name Camptopteridinae. 



As the affinities of Dictyophyllum are thus not yet settled 

 beyond dispute, I have made a renewed examination of the 

 Stockholm material of Dictyophyllum exile in the hope of dis- 

 covering some new details of interest. 



The number of sporangia in each sorus cannot be very 

 clearly seen in the material I have examined, on account 

 of the crowded position of the sporangia. Nathorst, how- 

 ever, has been able to state that the number is probably 4 — 7. 



On the question whether the annulus is complete or not 

 there are different opinions. The older writers, for instance 

 GÖPPERT and Schenk, speak of the annulus as complete, but 

 nowadays it is usually held to be incomplete (Zeiller 1893, 

 p. 97; Nathorst 1906, p. 13). 



In the specimens which I have examined, it is only rarely 

 that the whole extension of the annulus can be traced. The 

 whole annulus is shown only when the plane of the annulus 

 is parallel with the bedding of the rock and when it is at the 

 same time free of the adjacent sporangia. In pi. 2, figs. 13 — 16 



