28 THINNl'ELDIA. 



In 1853 Andrae' substituted Brongniart's genus Pachypteris 

 for TMnnfeUia, and spoke of Ettingshausen's type-species as 

 Pachypteris tUnnfeldia. The genus Paehjpteris is defined by 

 Brongniart as being cbaraoterised by entire pinnules, which are 

 either without veins or provided with a single vein. In some 

 large and well-preserved specimens figured by Zigno ' from Italian 

 Jurassic rocks, which are no doubt generically identical with 

 Pachypteris, the pinnules are traversed by several divergent veins. 

 Species of Pachypteris or Biehopteris, in which the ultimate 

 segments possess spreading and forked veins, bear a marked 

 resemblance to Thinnfeldia ; it is probable that the two genera 

 are very closely allied. In 1867 Sohenk' described examples 

 of ThinnfeUia from Khsetic beds of Franoonia, and published 

 drawings of the epidermal cells and stomata ; he placed the genus 

 among the Cycads. The most satisfactory evidence so far adduced 

 as to the systematic position of Thinnfeldia has been furnished by 

 Eaciborski * in his description and illustration of a specimen from 

 the Jurassic rooks of Poland. This author gives figures of a leaflet 

 bearing the impressions of what appears to be a circular sorus 

 showing the boundaries of individual sporangia. A specimen of 

 the genus in the British Museum (V. 5950) shows two rows of 

 contiguous polygonal prominences, one row on either side of the 

 midrib, which agree in size and shape with the son of recent 

 ferns ; but until we obtain sporangia we cannot speak with 

 certainty as to the precise nature of the fertile frond. 



In all probability Thinnfeldia is a fern, but we are unable, 

 through lack of good fertile specimens, to determine its family 

 position. The Ehsetio fronds from Scania described by Nathorst 

 as species of his genus Ptilozamiles " no doubt belong to plants 

 closely allied to Thinnfeldia. Some American Permian specimens 

 recently referred by Sellards " to a new genus Glenopteris might, 

 I think, be fairly included in Thinnfeldia. 



> Andrae (53), p. 43. 

 '^ Zigno (56), pis. xii., xiii., xv. 

 ' Schenk (67), p. 105, pi. xxTii. 

 * Eaciborski (94), pi. xx. figs. 1- 

 ■■' Nathorst (78), pis. xii. etc. 

 ^ Sellards (00), pi. xxxix. 



