368 FILICALES [CH. 



Thyrsopteris elegans (fig. 229, A, p. 294). The sori are partially enclosed in 

 a cup-like iiidusium and the sporangia appear to have an oblique annulus. 

 Venation and habit of frond of the Spkenopteris type. 



The pinna shown in fig. 271 is the type-specimen of 

 Spkenopteris arguta Lind. and Hutt. from the Yorkshire 

 Inferior Oolite and is indistinguishable from the English 

 examples on which Brongniart founded his species S. hymeno- 

 phylloides. Fig. 272 shows a specimen from the York Museum 

 illustrating the difference between the sterile and fertile pinnae. 

 The resemblance of some fertile pinnae of Coniopteris hymeno- 



Fic. 271. Conioplrris hyvienophylloides (Brongn.). Nat. size. From a specimen 

 in the Manchester Museum. 



phylloides to those of Thyrsopteris elegans has led to a frequent 

 use, without any solid justification, of the generic name of the 

 Juan Fernandez fern for Jurassic and Wealden plants. It is not 

 impossible that some of the fossils described by Heer from 

 Jurassic rocks of Siberia' as species of Tliyrsopteris are Cya- 

 theaceous ferns, but it is impossible to say with certainty that 

 they are generically identical with the recent species. In his 

 monograph of the Potomac flora of Virginia^ and Maryland, 

 Fontaine has described as species of Thyrsopteris several speci- 



1 Heer (76). - Fontaine (89). 



