250 MB. HAMSHAW THOMAS ON THE FOSSIL FLOBA OF [June I913, 



ferruginous concretions : some of these are balls of solid iron 

 peroxide, and others hollow boxstones showing concentric structure. 

 The ironstone-bed immediately above has been submitted to 

 chemical analysis, the chief constituents and their percentages 

 being as follows 1 : — 



Total iron, Fe 4290 



Fe 2 3 (51-28 



Si0 2 15-30 



Al 2 O a 4-88 



Water and organic matter 12'20 



In this ironstone bed the plants are splendidly preserved. Plants 

 occur, however, throughout the whole extent of the quarry where 

 the matrix is suitable for their preservation. The coaly and sand- 

 stone shales are also richly fossiliferous. On the same slab species 

 are often confusedly intermixed, making it difficult, if not im- 

 possible, to determine any zonal succession of forms. As the 

 Marske beds may probably be correlated with those in other parts 

 of North-East Yorkshire, much successful work may be done in the 

 investigation of the Jurassic flora in the near future. 



EXPLANATION OF PLATES XXIII-XXVI. 



Plate XXIII. 



Fig. 1. Marattiopsis anglica, sp. nov. Base of sterile pinna, showing rachis. 

 (Seep. 228.) Natural size. 



2. M. anglica. Part of sterile pinna, showing venation. Natural size. 



3. M. anglica. Part of fertile pinna, showing large synangia. Natural 



size. 

 4 a. M. anglica. Part of fertile pinna, showing smaller synangia. From 



the Naturhistoriska Riksuniseum, Stockholm. Natural size. 

 4 b. The same, enlarged three times to show the synangia. 



5. M. anglica. Remains of a single synangium, which had probably 



dehisced before preservation. From Roseberry Topping. X 6. 



6. Todites williamsoni Brongn. Part of sterile pinna, showing nervation. 



X2-5. (Seep. 228.) 



7. Nilssonia orientalis Heer. Part of a frond with an irregularly-lobed 



margin. (See p. 241.) Natural size. 



Plate XXIV. 



Fig. 1 a. Williamsonia spectabilis Nathorst. Part of a male flower, showing 

 sporophylls united at the base and bearing fertile segments above. 

 (See p. 230.) Natural size. 

 1 b. W. spectabilis. Part of a sporophyll, showing one of the small distal 

 lobes bearing synangia. From the counterpart of the specimen 

 shown in fig. la. X 2. 



2. W. spectabilis. Specimen of a male flower in the Naturhistoriska 



Riksmuseum, Stockholm, showing synangia on the lobes of the 

 sporophylls. Natural size. 



3. W. spectabilis (I) . Impression, possibly, of a separated young sporophyll. 



4. Pseudoctenis lanei, sp. nov. Part of a frond, showing the characteristic 



bases of the pinnaj. (See p. 242.) Natural size. 



Proc. Cleveland Nat. Field-Club, vol. i (1902) No. 5, p. 230. 



