26 ARKIV FÖR BOTANIK. BAND 13. N:0 T. 



Laccopteris? sp. 2. 



Pl. 3, figs. 18—20. 



The fragments shown in pl. 3, figs. 18 — 20, may be pro- 

 visionally referred to Laccopteris but, like those described 

 above, they cannot be specifically identified with any degree 

 of certainty. 



The venation of the present form differs from that of 

 the preceding one by showing very frequent anastomoses. 

 The meshes thus formed are very small, short and wide, and 

 thus the venation has not the parallel habit characteristic of 

 sp. 1. Some branches of the secondary veins are stronger 

 than the others and anastomose to form a series of large 

 meshes on each side of the midrib. There are no traces of the 

 fructifications. 



In regard to the venation these specimens show a great 

 resemblance to the Bathonian Microdictyon rutenicum Saporta 

 (1. c, p. 309; pl. 33, figs. 2—4; pl. 35, fig. 3; pl. 44, fig. 5), 

 which has also the same bow-shaped anastomoses of the stron- 

 ger secondary veins. It is possible, therefore, that the form 

 should rather be referred to the genus Microdictyon Sap. The 

 character of the venation mentioned is not very marked, 

 however, and it would appear as if the difference between 

 that genus and Laccopteris was not very distinct. Phlebo- 

 pteris Woodivardi Leckenby (1. c), which is brought by Saporta 

 (1. c, p. 313) to Microd/ictyon, is referred by Seward to Lacco- 

 pteris, and one of the figures given by that author (Seward, 

 1. c, p. 85, fig. 11 C) of another species, L. poly podioides, 

 shows a distinct approach to the Microdictyon-tyipe. 



There is another difficulty in the classification of these 

 ferns which may be mentioned here. Both Laccopteris and 

 Microdictyon are used for forms with a certain and in both 

 cases similar kind of fructification indicating decidedly lepto- 

 sporangiate affinities. It has been shown recently ^ that the 

 genus Nathorstia Heer, which has synangia of marattiaceous 

 nature, possesses a venation very like that of Microdictyon. 

 It is evident therefore that the character of the venation is 

 not a sufficient proof of generic identity with Microdictyon 



^ Halle, T. G., Some Mesozoic plant-bearing deposits in Patagonia 

 and Tierra del Fuego and their floras. K. Svenska Vet. Akad. Handl. 1913. 



