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OF THE GENERA NAVICULA AND CYMBELLA. 423 



Plate 28. 



(Magnification: Fig. 11, x 700 ; Figs. 12-19, x 1200.) 



Fig. 11. Cymhella {Encyonema) gracilis Rabli. Monmoutli. L 

 0-07, B. 0-009. Strio,e 13 in 0*01 mm., radiate, at 

 ends parallel, moniliform. Axial area linear, no cen- 

 tral area. Terminal fissures a sliojht distance from 

 ends. Slightly triundulate. Striae robust. No 

 stigma. Ends acute. Central nodule on dorsal side. 



12. Cymhella (Encyonema) Scotica W. Sm. Premnay Peat. 

 Herkimer. L. 0*04, B. O'OOS. Striae 13 in O'Ol mm., 

 radiate, lineate. Terminal nodules distant from ends, 

 turned downwards. Raphe much nearer to ventral 

 margin. Dorsal margin arcuate, ventral margin 

 nearly straight. Median stria on dorsal side with 

 stigma appearing to coalesce with central nodule. 

 Ends acute turned to ventral side. Hyaline zone 

 distinct, elongated round central nodule. 



13. Cymhella delicatula Kiitz. Herkimer. L. 0*04, B. 0*005. 

 Striae radiate, very delicate. Median stria on dorsal 

 side with distinct stigma. Ends acute. Terminal 

 nodules near ends. Ventral margin slightly arcuate, 

 dorsal margin arcuate. Hyaline zone very narrow, not 

 dilated. Central nodule on dorsal side. Intermediate 

 with Encyonema Scotica and very similar to it. 



14. Cymhella [Encyonema) gracilis-Cesatii. Herkimer. L. 

 0'04, B. 0'005. Rhomboidal, cymbelloid, ends acute. 

 Terminal nodules distant. Striae 20 in 0"01 mm., 

 radiate, punctate. Median stria on dorsal side 

 with distinct stigma. Central nodule on dorsal side, 

 ventral margin slightly gibbous, dorsal margin convex. 

 Areas indistinct. Terminal fissures comma-like, bent 

 towards ventral side. Sometimes still narrower and 

 longer. 



15. Cymhella (Encyonema) gracilis-Cesatii. Herkimer. 

 L. 0-045, B. 0-0045. Striae 18 in 0*01 mm., radiate, 

 punctate. Rhomboidal, ends acute, terminal nodules 

 distant from ends. Central nodule on ventral side. 

 Ventral margin slightly triundulate, dorsal margin 



JOURN. Q. M. C, Series II.— No. 83. 32 



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