524 CYCADOPHYTAN FRONDS [CH. 



lower edge curved abruptly upwards at the apex; the pinnae 

 are usually attached obUquely to the rachis but may be almost 

 at right-angles ; with the exception of the upper angle, the whole 

 of the base is attached to the frond-axis ; the base of the lamina 

 may be symmetrical, both angles being slightly rounded, or 

 asymmetrical, the upper or less frequently the lower corner being 

 auriculate (figs. 592, 593). There is no basal callosity on the 

 lamina nor is there a median sinus. The veins are more or less 

 spreading at the base but for the most part parallel. The features 

 of the epidermal cells and stomata are mentioned in the general 

 account of the genus. Fertile shoots of plants with this type of 

 frond are described under Williamsonia. Very little is known 

 of the stems which bore Ptilophyllum fronds, but as stated on 

 page 488 Indian specimens show leaves of Ptilophyllum cutchense 

 attached to a piece of stem (fig. 579) having the characters of 

 Bucklandia and characterised by a xylem-cylinder denser than 

 ia recent Cycads ; the structure of the wood at least in the Indian 

 stem is rather pycnoxylic than manoxylic. 



The fronds grouped under Ptilophyllum pecten are very widely 

 distributed in Jurassic floras ; they . are recorded from many 

 locaUties in Europe, from Turkestan^, India, Graham Land^, 

 Patagonia*, and elsewhere. 



As thus defined this ' species/ or more correctly this group of 

 forms, undoubtedly includes more than one species in the strict 

 sense, but without additional data it is maintained that the 

 recognition of clearly defined specific types or varieties is beyond 

 our power. It may be urged that in view of the wide geographical 

 range of the Ptilophyllum pecten type of frond and the admitted 

 probability that several species in the narrower sense are repre- 

 sented, distinctive specific names should be retained even though 

 under such designations are included forms that, so far as can 

 be seen from impressions, exhibit no constant distinguishing 

 features. My purpose is to emphasise the futility of attempting 

 to found well-marked species on the available material. The 

 student must decide for himself what course to pursue, whether 

 to retain such a specific name as cutchense for the Indian fronds 



1 Seward (07") p. 29. ^ Nathorst (04=) B; Halle (IS^). 



= HaUe (13). 



