180 BRITISH DESMIDIK^. 



their centre, and are precisely like those of Clostet^ium except in their 

 aggregation, which is the only distinction between the two genera. 



1. A. falcatus (Corda) ; bundles of numerous crescent-shaped very 

 slender cells. 



Micrasterias falcata, Corda, Ahnanach de Carlsbad 1835, p. 121. t. 2. f. 29. 

 Closterium gregariuin, Meneghini, Consp. AJg. Eiigan.^. \7 (18.S7). 

 Xanthidium? diforme, Ehr. Infus. p. 14/. t. 10. f. 26 (1838)? 

 Clostermm faJcatvm, Meneghini, Synop. Desniid. in Linncea 1840, p. 233. 

 Rhaphidimn fascicidatum, Kiitzing, PhycoJogia Germanica, p. 144 (1845). 

 Anhistrodesmiis gregarius, Brebisson, in lit. cum specimine (1846). 



Dolgelley and Penzance, J. R. Sussex, Mr. Jenner. Ambleside, Mr. 

 Sidebotham. 



Italy, Meneghini. Germany, Eh'enherg, Kiitzing. Falaise, Brebisson. 



Cells very minute and slender, crescent-shaped, fasciculated in irregular 

 bundles composed of numerous individuals, which, as the convexity of each is 

 turned inwards, diverge at each extremity of the bimdle. 



This plant is not unlike an early state of a Closterium, and as such I 

 formerly considered it ; but Corda, Kiitzing and Brebisson have pronounced 

 it to belong to a distinct genus. 



The bundles vary greatly in their compactness, as well as in the number of 

 their cells. 



Not having seen Corda' s description and figure of Ankistrodesmus convo- 

 lutus, I am unable to determine Avhether the present species differs from it. 



Length of cell -g\-^ of an inch ; greatest breadth yttz- 



Tab. XXXIV. fig. 3. a, b, c. aggregated cells ; d. a single cell. 



**** Frond composed offevj cells, definite in number ^ and not forming 



a filament. 



19. PEDIASTRUM, i^/e^/e/^. 



Frond plane, circular, composed of several cells, which form by their 

 union a flattened star, and are generally arranged either in a single 

 circle or in two or more concentric ones ; marginal cells bipartite. 



Frond minute, composed of four or more cells united together in 

 the figure of a flattened star ; when these are only four in number 

 they are not ai'ranged in a circle and the star is somewhat angular ; 

 in most species, however, they form either a single circle or two or 

 more concentric ones, and one or two cells usually occupy the centre. 

 The cells are combined into a frond by a mucous matrix, which is 

 generally colourless and constitutes hyaline interstices. Occasionally 

 some are ruptured, but in this case their endochrome alone escapes, 



