442 BENNETTITALES [CH. 



the depressions and these show the same decrease in size when 

 traced from the free segments to the cupular organ. Nathorst 

 obtained microspores only from the larger projections and none 

 from the smaller, a circumstance which may indicate that only 

 the upper and larger synangia were fully developed^. 



This species is especially interesting as throwing Ught on the 

 nature of one of the specimens (from the Whitby Museimi) figured 

 by Williamson as a 'carpellary disc^': the 'seeds' of Williamson 

 are no doubt, as Nathorst believes, synangia, while the smaller 

 pairs of markings figured by Williamson represent rudimentary 

 synangia and not 'abortive ovules.' Though the specific identity 

 of Wilhamson's specimen and WilUamsonia whitbiensis is not 

 certain, the latter is undoubtedly a closely allied form of a micro- 

 sporophyll-verticil. A specimen figured in 1900 as a flower of 

 Williamsonia pecten^, designated by Nathorst WilUamsonia sp., 

 is a very similar if not an identical type; it consists of a fairly 

 deep basal cup the surface of which is characterised by the presence 

 of several regular ridges between which are pairs of small depres- 

 sions containing carbonaceous matter. In the light of Nathorst's 

 researches it is clear that this is an incomplete example of a whorl 

 of microsporophylls. The base of the disc is incomplete, but it 

 is certain from the small size of the basal hole with torn edges 

 that the cup could not have been attached to the base of a recep- 

 tacle as are the microsporophylls in Wieland's bisporangiate 

 flowers of Cycadeoidea. The specimens referred by Nathorst to 

 Williamsonia pecten^ (Leek, ex farte) are similar to those described 

 as W. whitbiensis, but differ in the texture of the cup and in the 

 degree of cuticularisation of the synangial walls. The synangia 

 of W. fccten are of the usual reniform type and multicellular as 

 in W. spectabilis. 



1 Nathorst (12) p. 7. ^ Williamson (70) PI. m. fig. 1; PI. un. fig. 2. 



' Seward (00) B. p. 201, PI. n. fig. 7. 



* Nathorst (11) p. 19, PI. V. figs. 1 — 8; Pl.vi.figs.l — 3. The name Potoeozamio 

 pecten was applied by Leokenby [Leokenby (64) A. p. 77, PI. IX. fig. 47] both to the 

 fronds and an associated flower which is now recognised as a whorl of microsporo- 

 phylls. I formerly employed the name WilUamsonia pecten for fronds and flowers, 

 but in view of Nathorst's work it is advisable to follow his example and to use 

 separate names for male and female flowers when there is no proof that they belong 

 to one type ; similarly the fronds may conveniently be spoken of as Ptilophyllum 

 pecten. 



