BRITISH DESMIDIE.E. 77 



Dolgellcy, J. R. Fittleworth near Petworth, Midhvxrst, and Ashdown 

 Forest, Sussex, Mr. Jenner. Ambleside, Mr. Sidebotham. Aberdeen, Mr. 

 P. Grant. 



West Point, New York, Bailey. 



Frond smooth, nearly as large as that of Micrasterias Crux-Melitensis, and 

 convex at its ends. Segments deeply constricted ; lobes horizontal, conical 

 and bidentate at the apex, the basal ones longest. 



The transverse view is fusiform, with two teeth at each end and a small cir- 

 cular central opening at the connexion of the segments. Endochrome green 

 with scattered vesicles. The empty frond is minutely pimctate. 



From the resemblance of this plant to Ehrenberg's figure of young M. Ci'ux- 

 Melitensis, I at first considered it the immature state of another species ; but 

 haA-ing repeatedly gathered it unmixed with any species of Micrasterias to 

 which it could belong, and Avatched it carefully for some time without detecting 

 any alteration, I am obliged to consider it as distinct. Its size alone would 

 forbid the supposition that it belonged to M. Crux-Melitensis ; it is thicker 

 than any other species of Micrasterias, and finally its starch vesicles are too 

 abmidant for a young plant. Subsequently Mr. Jenner gathered it in Sussex, 

 and he fully agrees with my opinion that it is a cUstinct species. 



Mr. Hassall, who separates it from Micrasterias, has overlooked the biden- 

 tate extremities of the lobes, notwithstanding their presence in the Dolgelley 

 specimens, from which his figure was taken. 



Length of frond }-^ of an inch ; breadth of basal lobe -^ ; breadth of 

 end lobe -^^. 



Tab. X. fig. 2. a. frond with endochrome ; b. empty frond ; c. transverse 

 view. 



13. M. pinnatifida (Kiitz.) ; frond plane, its ends straight ; segments 

 deeply constricted ; lobes horizontal, triangular, bidentate. 



Euastrum (No. 7), Bailey, Amer. Bacill. t. 1. f. 29. (1841). 

 Euastrum pinnatifidum, Kiitz. Phycologia Germ. p. 134. (1845). 



Hab. Dolgelley, /. R. Ambleside, Mr. Sidebotham. 



United States, Bailey. Germany, Kutzing. Falaise, Brebisson. 



The frond is very minute and plane ; its segments are deeply constricted, 

 and straight or slightly concave at the end. The lobes are horizontal, trian- 

 gular and bidentate at the apex, the basal ones longest. 



M. 'pinnatifida is a much smaller species than M. oscitans, but resembles 

 it in form. Tlie surface however is flatter, the end margin is straight or 

 slightly concave instead of convex, and the lobes are more tapering so as to 

 appear triangular ; the colour also is paler. 



I have not detected starch vesicles in this plant, and might have taken it for 

 the young state of M. Crux-Melitensis, but its form is so similar to that of 

 M. oscitans, that the claim of the latter undoubted species to be considered 

 distinct would be invalidated if M. pinnatifida should be proved an immature 

 state of M. Crux-Melitensis. 



