BRITISH DESMIDIEiE. 71 



striction -^ ; diameter of sporangium from ^ J-y to -^ ; length of spine from 



TTTg' ''" 7 4 1- 



Tab. VII. fig. 1. a. mature frond ; b. dividing frond j c, d, e and/, different 

 stages of sporangia ; </. sporangium magnified 400 times. 



2. M. rotata (Grev.) ; frond orbicular, smooth ; segments five-lobed ; 

 lobes dichotomously incised, ultimate subdivisions bidentate. 



EchineUa rotata, Greville, in Hookers Brit. Fl. v. 2. p. 398 (1830). 

 Euastrum Rota, Ehr. Abh. derBerJ. Ak. (1831), p. 82 ; Infus. t. 12. f. \.c,e. 



Kiitzing, Phijcoloyia Germanica, p. 134. 

 Eutomia rotata, Harvey, Manual of Brit. Algae, p. 187 (1841). 

 Micrasterias rotata, Ralfs, Annals of Nat. Hist. v. 14. p. 259. t. 6. f. 1 



(1844) ; Trans, of Bat. Soc. of Edinburgh, v. 2. p. 131. t. 10. 



Common. Appin, Capt. Carmicliael. North and South Wales ; Dartmoor 

 and Penzance, J. R. Sussex, Surrey and Kent, 3Ir. Jenner. Near Bristol, 

 Mr. Broome. Aberdeen, Dr. Dickie. Ambleside, Mr. Sidebotham. 



Germany, Ehrenberg . Falaise, Brebisson. Rhode Island, Bailey. 



M. rotata is very similar to M. denticulata, but differs from it in having 

 the ultimate subdivisions dentated. The end lobe is usually slightly exserted, 

 and the middle lobes have eight subdivisions instead of four ; I have never- 

 theless some doubt whether this plant is not a variety of 31. denticulata, as 

 the angles are sometimes merely acute instead of being prolonged into teeth. 



Length of frond -^ of an inch ; breadth yij. 



Tab. VIII. fig. 1. a. frond v^^ith endochrome ; b. empty frond. 



3. M. fimbriata, ; frond orbicular, smooth ; segments five-lobed ; 



lobes dichotomously incised ; ultimate subdivisions obtusely emar- 

 ginate, spinoso-mucronate. 



Micrasterias Rota, in part, Ehr. Infus. t. 12. f. d. (1838). 

 In a boggy pool near Dolgelley, /. R. 

 Germany, Ehrenberg. 



The frond is large and circular ; the segments five-lobed ; the end lobe 

 linear-cuneate, having a broad shallow notch and two or three spines or mucros 

 at each angle, the angles rounded. As in the preceding species, the lateral 

 lobes are dichotomously incised, but their incisions are more shallow, the 

 ultimate subdivisions rounded and slightly emarginate, and each furnished with 

 two spines, w-hich are often curved. 



The basal lobes are twice and the middle lobes usually three times dichoto- 

 mous, consequently the latter may have eight subdivisions whilst the former 

 have only four. The end lobe is somewhat exserted, and frequently also there 

 is an elongation of the subdivisions of the basal lobes which border the central 

 constriction. 



Length of frond y^-g of an inch ; breadth ■^\^. 



Tab. VIII. fig. 2. a. empty frond ; b. frond with endochrome. 



