348 



cases the colonies are embedded in a copious mucus. The cells 

 are elongated, fusiform or lanceolate, with attenuated extremities, 

 or sometimes sigmoidal in form. The chromatophore is almost 

 homogeneous, of a pale blue-green colour, and somewhat lateral in 

 position. Division of the cells occurs much as in Dactylococcus, 

 by oblique septation. 



D. montana W. & G. S. West (length of cells 8'6 11 '5 p., breadth 3'5 4 p ; 

 fig. 162 A) occurs in bog-pools amongst Sphagnum. D. rhaphidioides Hansg. 

 is known from the plankton of Lough Neagh. 



Genus Merismopedia Meyen, 1839. This is one of the most 



striking genera of the 

 Chroococcacese, consist- 

 ing of a flat rectangular 

 colony, the cells of which 

 are arranged in rectilinear 

 series. Cell-division takes 

 place in two directions 

 and the cells appear to 

 be usually arranged in 

 groups of four. The cells 

 are globose, ellipsoidal, or 

 oblong, sometimes slightly 

 angular by compression, 

 and the cell-contents are 

 homogeneous. 



Fig. 162. A, Dactylococcopsis montana 

 W. & G. S. West, from Widdale Fell, W. Yorks. 

 B, Merismopedia glauca (Ehrenb.) Nag., from 

 Thursley Common, Surrey. C, M, elegans 

 A. Br., part of a large colony from Wicken 

 Fen, Cambridge. D, Tetrapedia Reinschiana 

 Arch., from near Goring, Oxford. (All x 450.) 



M. glauca (Ehrenb.) Nag. 

 is the commonest British 

 species, occurring in ponds, 



ditches, bogs and lakes; diam. of cells 3'3 3'8/n; fig. 162 B. M. punctata 

 Meyen and M. ceruginea Breb. are not infrequent in stagnant water. M, 

 elegans A. Br. is the largest species of the genus and is known from few 

 localities in the British Islands; diam. of cells 6'5 9-5 p.; fig. 162 C. The 

 colonies of M. gloMca and M. elegans often reach a large size (diam. up to 

 220 /i) and may contain as many as 1856 cells. 



Genus Tetrapedia Reinsch, 1867. In this genus the cells are 

 of some definite and symmetrical shape, often constricted into two 

 equal half-cells. The cell-wall is firm and the cell-contents are 

 homogeneous. In some species the cells are almost invariably 

 solitary, but in others they are grouped in flat colonies similar to 

 those of Merismopedia. 



