NiLssojriA. 229 



retained, but as we possess the type-specimens of Leckenby his 

 sijecific designation mediana may he used in preference to the 

 ■okler term. 



Some of the best examples of Nihsonia mediana, other than 

 those in the British Museum, are in the Leckenby Collection, 

 Cambridge. 



39,293. PL IV. Fig. 1. 



This frond measures 20 cm. in length, and illustrates the larger 

 foim of the species. The segments vary considerably in breadth ; 

 thoy are distinctly broadened at the base, and longer iu proportion 

 to their width than in Nihsonia coinpta. The simple parallel veins 

 arc clearly preserved. 



39,290. PL IV. Fig. 2. 



Erond 18 cm. long, with very narrow segments, about 4 cm. long 

 and 3-6 mm. broad ; more acutely pointed than in 39,293, The 

 raohis is represented by a shallow groove. This type of frond was 

 named hy Leckenby Pteropliyllum angustifolium, and the specimen 

 is so labelled by Bean ; a comparison of several specimens in the 

 Leckenby and British Museum Collections leads me to unhesitatingly 

 regard this form of frond as specifically indistinguishable from 

 Nihsonia mediana. 



Upper Shale, Scarborough. 



39,298. PL IV. Fig. 3. 



A frond 20 cm. long, illustrating the very unequal breadth of 

 the segments. Associated with fragments of Tmniopteris vittata. 



V. 3558. PL IV. Fig. 4. 



A still narrower frond, m which the apical portion has been 

 preserved. This specimen shows the finer texture of the segments 

 as distinguished from the thicker and coarser segments of N. compta. 

 Labelled by Bean Pterophjllum angustifolium. 



Gristhorpe Bay. 



Other specimens : — 39,2di, 39,308, 39,309 (also Taniopferis 

 vittata). 



