416 SIR NICHOLAS YERMOLOFF OX. SOME INTERMEDIATE FORMS 



Encyonema Scotica (Plate 28, fig. 12). 



This form is common both in European and American deposits. 

 It is too well known to need description. The striae are less 

 dense and the areas more distinct. 



Encyonema gracilis (Plate 27, fig. 10 ; Plate 28, fig. 11). 



I describe here only those specimens of this species which are 

 fossil in the Monmouth and Cherryfield slides. I think I have 

 made no mistake in the determination, but I am not quite sure : 

 it comes also very near to Cymhella Yarrensis, figured in Schmidt's 

 Atlas. On the other hand Cleve states that Cymhella Yarrensis 

 is a native of Australia and Tasmania, and I am rather averse 

 to identifying a fossil form from North America with a living one 

 from southern waters. The specimens are rather large and robust, 

 the striae pronounced, radiate but parallel at the ends. Axial 

 area very regularly linear. Ends acute with slightly distant 

 terminal nodules. Tendency to triundulation slight but 

 appreciable. No distinct stigma, but on some specimens there is 

 something like an indistinct stigma. Striae moniliform slightly 

 decipient. Length as large as 0*07 mm., or even more, therefore 

 these American fossil specimens are longer than stated by Cleve, 

 who gives as maximum length 0'056 mm. Striae visible even 

 under low power. The number of striae to O'Ol mm. seems 

 identical with the one stated by Cleve : 13 to 0*01 mm. or a 

 little more. 



Cymbella angustata (Plate 27, fig. 9). 



This is a very important member of our series. It is fouiid 

 both in European and American slides. The striae are faint, 

 radiate, about 16 to O'Ol mm. Ends rostrate-capitate. Margins 

 usually triundulate. Areas narrow but distinct, and in forms 

 intermediate to Cymhella Stodderi showing a tendency to become 

 broader. 



About this species there seems to have arisen in the works of 

 authors some confusion : on Plate XVII, fig. 156, of the Synopsis 

 of British Diatomaceae, the Rev. Wm. Smith gives a fairly good 

 drawing of it, but calls it Navicula angustata, which is natural 

 enough owing to its nearly symmetrical outline. He does not 

 show any striae. But the whole habit of the species seems 



