76 BRITISH DESMIDIEiE. 



and the absence of teeth on the lateral ones, but I have seen some specimens 

 which make it doubtful whether they be really distinct. 



One figure of it was engraved as the young state of M. denticulata, before 

 reasons nearly similar to those which I have stated imder the foregoing spe- 

 cies had induced me to describe it as distinct. 



Length of frond -^^ of an inch ; breadth -g-g-g • 



Tab. VII. fig. 2. and Tab. X. fig. 4. a. frond with endochrome ; b. empty 

 frond. 



**** Fronds oblong. 



1 1 . ilf . Jenneri ; frond oblong, minutely granulated ; segments five- 

 lobed, lobes closely approximate, cuneate, lateral ones obscurely 

 bipartite, the subdivisions emarginate. 



a. Granules appearing like mere puncta. 



yS. Granules larger, giving a dentate appearance to the margin. 



a. Greatham Bogs, Fittleworth, and Ash down Forest, Sussex, and near 

 Southampton, Mr. Jenner. Dolgelley, J. R. 



/3. Medhurst, and Ashdovra Forest, Sussex, Mr. Jenner. 



Fronds large, tvdce as long as broad, oblong or quadrilateral. Segments 

 five-lobed ; lobes cuneate, approximate, lateral ones slightly bipartite and the 

 subdivisions truncato-emarginate. Endochrome green with scattered vesicles. 

 The transverse view of the frond fusiform. 



The surface of the frond is furnished with minute pearly granules which 

 usually look like mere puncta, but in some specimens gathered by Mr. Jenner 

 in Sussex they are larger and give the margin a dentate appearance. 



This puzzling plant almost seems to unite Micrasterias with Euastrum. It 

 agrees vdth the latter genus in figure, and the lobes also at first sight appear 

 more like those of a species of Euastrum than one of Micrasterias ; but they 

 have incisions, although mconspicuous, which divide them into two portions, 

 each slightly emarginate. A transverse view shows the absence of the inflated 

 protuberances always found in true species of Euastrum. 



Micrasterias Jenneri differs from all other species of Micrasterias in its 

 oblong fronds. It may easily be distinguished from Euastrum verrucosum 

 and E. crassum by its five-lobed segments, and from E. obIon</um not only 

 by its more quadrangular form, but by the lobes being so closely in contact as 

 almost to conceal the separating sirmses. 



Length of frond yiy of an inch ; breadth -^-i-g . 



Tab. XL fig. 1. a. frond with endochrome ; b. empty frond; c. frond mag- 

 nified 400 times ; d. transverse view. 



***** Lobes horizontal, attenuated, bidentate. 



12. M. oscitans (Ralfs) ; frond with convex ends ; segments con- 

 stricted ; lobes horizontal, conical, bidentate. 



Micrasterias oscitans, Ralfs, in Jenner' s FL of Tunbridge Wells, p. 198 



(184.5). 

 Holocystis oscitans, Hassal), Brit, Freshwater Algce, p. 386. t. 90. f. 4. (1845). 



