Yol. 69.] 



THE CLEVELAND DISTRICT OF YORKSHIRE. 



235 



collections here described contain a similar large series of fronds 

 "which are, for the present, all included under this species. Several 

 well-marked varieties occur ; but, as at Whitby, 1 they seem to be 

 connected one with the other by intermediate forms. It is probable 

 that future work on the structure of the cuticles of these forms 2 

 will show that the principal varieties may be regarded as distinct 

 species. I hope to undertake the detailed investigation of this 

 question, when further specimens have been obtained in a suitable 

 state of preservation. 



The form and nervation of some characteristic pinnae are shown 

 in figs. 3 & 4. The pinnas are for the most part attached to the 



Pig. 4. — Another type of frond of Ptilophyllum (Williamsonia) 

 pecten, showing the basal lobes of the pinnce. Natural size. 



rachis by a broad portion of their bases. In some of the larger 

 examples, there is a well-marked basal lobe on the lower (see 

 fig. 4) or upper margin ; specimens showing the latter characteristic 

 approach nearly to the Otozamites type, while the Ptilophyllum 

 type is the commonest (see fig. 3, p. 234). A more detailed con- 

 sideration of the group is reserved for a future occasion. 



T^niopteris vittata Brongn. 



[' Hist. V<%6t. Foss.' 1828, p. 263 & pi. Ixxxii, figs. 1-4.] 

 This very common Yorkshire fossil is represented at Marske by 

 a number of specimens showing the usual form and bifurcating 



1 See Seward (00) p. 190. 



2 The epidermis of the fronds of the type shown in fig. 3 B (p. 234) was 

 thickly covered with circular hair-scars. 



