74 BRITISH DESMIDIE^. 



Mierasterias melitensis, Menegh. Synop. Desmid. in Linncea 1840, p. 216. 



Ilab. Pools, very rare. Dolgelley, J. R. Congleton, Cheshire, and Arable- 

 side, Westmoreland, Mr. Sidebofham, Henfield, Mr, Jenner. 



Germany, Ehrenherg. Falaise, Brebisson. Maine to Virginia, Bailey. 



The frond is about the size of that of M. fur cat a and similarly divided, 

 but the incisions are less deep, the subdivisions stouter and less divergent, and 

 their extremities are bidentate rather than forked ; the end lobe also is more 

 suddenly contracted beneath the bifurcation. The colouring matter extends 

 nearly to the margin. 



Mr. Jenner finds the empty fronds very delicately punctated. 



Length of frond ^h^ of an inch ; breadth g-lr- 



Tab. IX. fig. 3. a. frond with endochrome ; b. empty frond. 



8. M. morsa ; frond angular-elliptic ; segments three-lobed, end 



lobe with bipartite angles ; lateral lobes broad, margin concave in- 

 ciso-serrate. 



Euastrum (No. 4), Bailey, Amer. Bacil. t. 1. f. 25. 



a. Serratures distinct. 



y8. Serratures obscure. 



Hab. a. In a bog near Llyn Gwernan, Dolgelley, /. R. 



j3. Pools near the Quaker's Chapel, Dolgelley, /. R. Ashdown 

 Forest, Mr. Jenner, 



New York to Virginia, Bailey, 



The frond of Mierasterias morsa is as large as that of M. Crux-Melitensis. 

 The segments are three-lobed ; the end lobe is broad, cuneate and somewhat 

 exserted, has a broad shallow notch, and at each angle is bifid ; the divisions 

 are narrow, and each terminated by two or three minute teeth. The lateral 

 lobes are broad and cimeate, and their margm is concave, symmetrically incised 

 and serrated. 



In /3. the characters are less strongly marked, the lateral lobes are waved 

 rather than toothed, and also more irregular. 



Mierasterias morsa diifers from M. Crux-Melitensis in the bifid angles of 

 the end lobes and in the concave and serrated margin, as well as the less-di- 

 vided state of the lateral lobes. The concave margin of the lateral lobes pro- 

 duces a more angular appearance of the frond than in the other species, and 

 the plant, especially in the variety /3, acquires some similarity of outline to 

 Euastrum verrucosum, but its serrated margin and the bifid angles of its end 

 lobes oblige me to place it in Mierasterias. 



Length of frond ^-L. of an inch ; breadth -g-j-j. 



Tab. X. fig. 1 . a. frond with endochrome ; b, c. empty fronds ; d, e. fronds 

 of R. 



