416 DIATOMACE.fi. 



of the end view of these, will distinguish this plant from all 

 other freshwater species. 



It is of a pale brown when recent, becoming in drying of a 

 greyish hue with a silvery lustre. 



73. EUNOTIA Ehr. 



Char. Frustules free, striated laterally, with two superficial 

 grooves running round each, and indicated by lateral 

 puncta. 



This genus differs only from Fragilaria in that the frus- 

 tules never form filaments, as in that genus. 



1. EUNOTIA ARCUS Ehr. 

 Plate XCVII. Fig. 5. 



Char. Frustules elongated, striated. In front view qua- 

 drangular, with straight sides. In lateral aspect narrow, 

 curved, constricted towards either extremity. 



Eunotia Arcus, Bericht. der Akademie d. Wissensch. zu 

 Berlin, 1837, p. 45. ; Ehr. Die Infus. t. 21. fig. 22. ; 

 Eunotia monodon? Ehr. ; Ralfs, in Annals, vol. xv. p. 459. 

 pi. xiv. fig. 1 ? ; Jenner, in loc. cit. p. 202. 



Hab. Cheshunt : A. H. H. Piltdown Common : Mr. 

 Jenner. Penzance : Mr. Ralfs. 



A distinct and not uncommon species. 



2. EUNOTIA DIODON Ehr. 

 Plate XCVII. Fig. 6. 



Char. Frustules elongated. In front view quadrangular, 

 with straight sides. Convex margin of lateral aspect 

 Indent ate. 



Eunotia Diodon, Bericht. der Akad. d. Wissensch. zu Ber- 

 lin, 1837, p. 45. ; Die Infus. p. 192. t. xxi. fig. 13. ; 



