460 Mr. J. Ralfs on the British species of Eunotia. 



The frustules are very minute, but vary greatly in length, being 

 in some specimens only twice as long as broad, and in others six 

 or seven times longer than broad. 



The front view has its ends slightly rounded and its puncta 

 very obscure. In the lateral view the shorter frustules are more 

 turgid on the back, and more constricted near the ends. Although 

 the frustule seems in general to have no strife, I believe that this 

 apparent deficiency is owing to the minute size of the specimens 

 which have come under my notice, as I have occasionally observed 

 very faint lateral striae. 



A frustule of this species, though very much smaller, has great 

 resemblance to a solitary frustule of Fragilaria pectinalis; but in 

 this plant the concavity of one margin is generally greater, and 

 the constriction near the ends of the frustule more considerable ; 

 the front view, too, is narrower in proportion to the lateral ; still 

 it may eventually prove to be only the commencement of that 

 plant. 



In the ' American Bacillaria^ there is no description of this 

 species, but as Bailey's figure represents a larger plant, with di- 

 stinct lateral strise, it is probably taken from a more mature spe- 

 cimen. 



Plate XIV. fig. 1. Eunotia monodon: a, front view; h, front view of 

 frustules deprived of their colouring matter ; c, lateral views. 



2. Eu. diodon, Ehr. Lateral view striated, with the convex margin 

 bidentate. Ehr. Infus. p. 192. t. 21. f. 23 ; Pritch. Infus. p. 214 ; 

 Bailey, I. c. pi. 2. f. 29. 



In freshwater pools, very rare. Penzance, /. R. ; Piltdown Com- 

 mon near Uckfield, Sussex, Mr. Jenner. 



Front view about twice as long as broad, with two distinct 

 puncta at each end, and the terminations of the lateral striae evi- 

 dent along the lateral margins. Lateral view much narrower ; the 

 margin on one side flat or slightly concave, on the other convex 

 with two rounded elevations and a constriction near each end ; 

 the lateral striae are very distinct. The transverse ridges on the 

 dorsum appear much more considerable in the shorter than in 

 the longer frustules. 



The figure in the ' American Bacillaria' represents a larger 

 plant than the specimens I have seen, but agrees with them in 

 other respects. 



This species difiers from Eunotia tetraodon in the number of 

 ridges on the dorsum, which is less rounded, and in having the 

 lateral surface much narrower than the front, and one of its mar- 

 gins flat or slightly concave. 



Plate XIV. fig. 2. Eunotia diodon: a, front view j b, lateral view. 



