52 Annals of the South African Museum. 



Until we find Avell-preserved fertile specimens of Pachyptcris, Ptilo- 

 zamites, Thinnfeldia, and other genera we cannot hope to define with 

 accuracy their systematic positions or relationships. One impression 

 derived from a comparison of Nathorst's Ptilozamitcs, of which there 

 is an exceedingly good series in the Stockholm Museum, with the 

 Southern Hemisphere Thinnfeldias is that the differences between 

 the two genera have been exaggerated, and geographical separation 

 has been allowed too much weight in influencing the choice of distinct 

 generic designations. On the other hand, it is clear that certain 

 authors have unduly extended the application of Ettingshausen's 

 Thinnfeldia. 



The most satisfactory evidence so far published as to the systematic 

 position of Thinnfeldia has been furnished by Eaciborski in his de- 

 scription and illustration of a specimen of T. rhomboidalis from Jurassic 

 rocks of Poland : this author gives drawings of a leaflet bearing the 

 impression of what appears to be a circular sorus showing the 

 boundaries of individual sporangia, but the material is too imperfect 

 to afford any indication as to the nature of the sporangia.* In addition 

 to the evidence afforded by the Polish specimen I may mention a 

 specimen in the British Museum (V. 5950) in which the broadly 

 linear segments of a Thinnfeldia pinna show two rows of contiguous 

 polygonal or oval prominences, one on either side of the midrib, 

 which agree in size and shape with the sori of certain ferns ; but 

 until we obtain sporangia we cannot speak with certainty as to the 

 precise nature of the fertile frond. My friend Mr. Arber, of Cam- 

 bridge, hopes to publish a more detailed account of the British 

 Museum specimen. 



Thinnfeldia odontopteeoides (Morris). 



Plate VII., figs. 1, 7, 8, 8a ; Plate VIIL, figs. 7, 8 ; Plate IX., 

 figs. 7, 8; Plate XI., fig. 2. 



Text-figure 6. 



1845. Pecopteris odontopteroides Morris, in Strzelecki's New South 



Wales, p. 249, pi. vi., figs. 2-4. 

 1847. Glciclicnitcs odontoiHeroidcs McCoy, Annals Mag. Nat. Hist.,. 



vol. XX., p. 147. 

 1872. Pecopteris odontopteroidcs Carruthers, Quart. Journ. Geol. Soc.,. 



vol. xxviii., p. 355, pi. xxvii., figs. 2, 3. 



» Eaciborski (94), pi. xx., figs. 1, 2, p. '206. See also Zeiller (00), p. 97. 



