xxi] 



DIPTERIDINAE 



393 



Hausmannia Richteri or may be a distinct species ; it shows 

 some of the finer veins connecting the shorter forked ribs, 

 which formed part of the reticulate ramifying system in the 

 mesophyll. This specimen was obtained from the plant-beds of 

 •Culgower on the Sutherlandshire coast, which have been placed 

 by some geologists in the Kimmeridgian series. 



The smaller type represented in fig. 278, E, is referred by 

 Richter to a distinct species, Hausmannia Sewardi^, founded 

 on a few specimens from the Lower Cretaceous strata of 

 Strohberg. This species is characterised by a stouter rhizome 



Fig. 289. Hausmannia sp. Upper .Jurassic, near Helmsdale, Scotland. From 

 a specimen in the British Museum. (Nat. size.) 



bearing smaller leaves consisting of a short petiole (3 — 4 cm. 

 long) and an obovate lamina (1 — 2 cm. long and broad). There 

 are usually two opposite leaflets on each leaf-stalk, and these 

 may be equivalent to the two halves of a single deeply dissected 



lamina. 



It is interesting to compare these different forms of Haus- 

 mannia with the fronds of recent species of Dipteris represented 

 in fig. 231. The more deeply dissected type, such as H. dicho- 

 toma, closely resembles D. Lohbiana or D. quinquefurcata, 

 while the more or less entire fossil leaves (fig. 278, E, F and 

 fig. 289) are very like the somewhat unusual form of Dipteris 

 conjugata shown in fig. 231, B, p. 297. 



1 Kichter (06) p. 22. 



