66 



CZEKANOWSKIA 



[CH. 



unknown in the genus (e.g. B. paucipartita). Some specimens which 

 may be identical with this type were obtained several years ago 

 by Dr Nathorst from Yorkshire 

 but never fully described : an 

 examination of his unpublished 

 drawings and of specimens col- 

 lected by Mr Hamshaw Thomas 

 convinced me that some forms 

 of Czekanoivskia are more freely 

 branched and exhibit more varia- 

 tion in the breadth of the lamina 

 than I had formerly supposed. 

 In specimens of the type first 

 noticed by Nathorst some of the 

 segments are comparatively broad 

 and fern-like, a feature that is 

 not seen in the leaves shown in 

 fig. 661. This species affords a 

 striking contrast to Czekanowskia 

 Murrayana in which the long 

 leaves are unbranched, and as 

 Nathorst 1 suggests the name 



Soknites might be revived for the unbranched type; but in the 

 absence of any difference in the epidermal characters, it would 

 seem undesirable to raise to generic rank a feature depending on 

 the simple or branched habit of the leaves of otherwise similar 

 leaf-fascicles. 



Czekanoivskia rigida Heer. 



This species, founded on specimens from Siberian Jurassic 

 rocks 2 , is characterised by its branched filiform leaves borne on 

 short shoots enclosed by scale-leaves, triangular or lanceolate in 

 form and in some specimens pendulous on slender stalks. Nathorst 3 

 states that the epidermal structure of the scale-leaves is similar 

 to that of the scale-leaves on short shoots of Ginkgo. The 

 characters of the stomata are mentioned in the account of the 



1 Nathorst (06) p. 11. 



2 Heer (77) ii. p. 70; (78) ii p. 7; (82) A. p. 19. 



3 Nathorst (06). 



FIG. 66 1. Czekanowskia microphylh 

 (Phillips). (British Museum No. 39 

 283; nat. size.) 



