392 FILICALES [CH. 



less deeply lobed into broad linear segments. The leaf is characterised by 

 dichotomously branched main ribs which arise from the summit of the 

 rachis as two divergent arms and radiate in a palmate manner, with 

 repeated forking, through the lamina. Lateral veins are given off at a 

 wide angle, and, by subdivision, form a fairly regular network similar to 

 that in Dictyophyllum, Clathropteris, and Dipteris. 



Hausmannia dichotoma, Dunker^. Fig. 288, A, B. 



This Wealden species, represented in the North German 

 flora and in beds of approximately the same age at Quedlin- 

 burg, has been discovered by Dr Marcus Gunn in Upper 

 Jurassic rocks on the north-east coast of Scotland. The lamina 

 (12 cm. or more in length) is divided into five to seven linear 

 segments and bears a close superficial resemblance to leaves 

 of Baiera and to recent species of Schizaea (fig. 222, p. 287). 

 Each segment contains one or two main ribs (fig. 288, A). A 

 similar form is described by Bartholin^ and by Moeller^ as 

 H. Forckammeri from Jurassic rocks of Bomholm. 



Hausmannia Kohlmanni, Richt. Fig. 278, F. 



In this species, instituted by Richter from material obtained 

 firom the Lower Cretaceous beds of Strohberg*, the compara- 

 tively slender rhizome bears fronds with petioles reaching a 

 length in extreme cases of 25 cm. but usually of about 

 10 cm. The lamina (1 — 7 cm. long and 1 — 10 cm. broad) is 

 described as leathery, obcordate, and divided into two sym- 

 metrical halves by a median sinus which, though occasionally 

 extending more than half-way through the lamina, is usually 

 shallow. The venation consists of two main branches which 

 diverge from the summit of the petiole (fig. 278, F) and sub- 

 divide into dichotomously branched ribs ; finer veins (not shown 

 in the drawing) are given off from these at right angles and 

 form more or less rectangular meshes as in other members of 

 the Dipteridinae and in such recent ferns as Polypodiwm 

 quercifolium (fig. 231, D, p. 297). 



The imperfect lamina represented in fig. 289 may belong to 



1 Dunker (46) A., Pi. v. flg. 1. = Bartholin (92) Pis. xi. xn. 



' Moeller (02) Pis. iv.— vi. * Kiehter (06) p. 21. 



