LICTYOPHYLLUM 139 



fragment of Clathropteris Mumteriana, Schenk, enlarged by Schenk 

 from the lower portion of a large frond, the venation becomes very 

 similar to the Dictyophyllum type. 



In Nathorst's description of the genus 1 attention is drawn to 

 the extreme variability of the species, and the consequent difficulty 

 of determining specific and variety limits. 



Schenk, in Zittel's "Handbuch der Palaeontologie," 2 includes 

 Goppert's genus Thaumatopteris under the generic term Dictyo- 

 phyllum. Bartholni, 3 in a recent contribution to the fossil flora 

 of Bornholm, has referred certain specimens to Hausmannia, 

 Dunk., which I am inclined to regard as DictyopJiyllum fronds. 

 This author considers that Dunker's genus should be retained 

 for certain forms of reticulately veined leaves ; his figures of 

 leaf fragments sufficiently demonstrate the great variation in 

 the form of the lamina of such leaves. Bartholni's figures of 

 Hausmannia Forchhammeri, Earth., 4 agree closely with those of 

 H. dichotoma as given by Dunker 5 and Schenk 6 ; in the description 

 of the Bornholm fossils no reference is made to this close resem- 

 blance to Schenk's North German specimens. So far as it is 

 possible to base any definite opinion on such small specimens 

 as those in the British Museum Collection, it is very probable 

 that Hausmannia Forchhammeri, Barth., and Dictyophyllum 

 Roemeri, Schenk, may be the same plant. The nature of 

 Dunker's genus, Hausmannia 1 is far from clear ; in the 

 " Wealdenbildung " the type specimen of this genus is figured, 

 but unfortunately there is no detailed description or drawing 

 of the venation. In habit the plant may be compared to Dic- 

 tyophyllum acutilolum* Schenk, from which it is distinguished 

 by the longer and narrower segments. Schenk makes use of this 

 doubtful genus for some small fragments found in the North 

 German Wealden rocks, 9 but his figures are by no means con- 



Foss. Fl. Schwedens, p. 13. 



Vol. i. p. 138. 



Bot. Tids. Bot. For. Kjovenhavn, vol. xviii. Heft i. 1892, p. 26. 



Loc. cit. pi. xi. figs. 4-6 ; pi. xii. figs. 1-3. 



Wealdenbildung, pi. v. fig. 1. 



Palaeontographica, vol. xix. pi. xxix. figs. 8 and 9 ; pi. xxxi. fig. 3. 



Wealdenbildung, p. 12. 



8 Fl. foss. Grenz. Keup. Lias, pi. xx. 



9 Palseontographica, vol. xix. p. 223, pi. xxix. figs. 8 and 9. 



