PEDIASTRUM. 391 



M. Boryana Ehrenberg, Infus. p. 157. pi. xi. fig. 5* i, b. 



Micrasterias tricyclia, pi. xi. fig. 8. a, but not b, c, d, 



e, f, g, h, i, k. 

 Hob. In a pond in a brick-field Netting Hill : A. H. H. 



This appears to me to be a very distinct species. The 

 central cells are not always placed in exact apposition with 

 each other, frequently intervals or triangular interstices are 

 left between them. Ehrenberg has strangely confounded 

 the Pediastrum Boryanum with this species, and on the other 

 hand this species with P. Boryanum. 



6. PEDIASTRUM ANGULOSUM Hass. 



Plate LXXXVI. Fig. 14. 



Char. Fronds constituted of two concentric circles of cells 

 surrounding a single central cell, the first circle being 

 formed usually of five cells and the second of ten. Mar- 

 ginal cells alone incised. 



Micrasterias angulosa Ehr., Infus. p. 158. pi. xi. fig. 6. Pe- 

 diastrum Boryanum Ralfs, loc. cit. p. 470. pi. xii. fig. 7. 

 in part 1. 



Hab. England. 



There can be scarcely a doubt of the distinctness of this 

 species. It is figured by Mr. Ralfs as the Micrasterias Bory- 

 ana Ehr., with which species it has no affinity. Mr. Ralfs' 

 figure accords closely with Ehrenberg's of Pediastrum. an- 

 gulosum. 



7. PEDIASTRUM CONSTRICTUM Hass. 

 Plate LXXXVI. Figs. 15, 16. 



Char. Frond large, composed of two or three concentric circles 

 of cells surrounding a single central cell, five cells in the 

 inner circle, ten in second, and fifteen in the outer circle. 

 Marginal cells toothed, teeth constricted. 



Pediastrum Boryanum var. Ralfs, in Annals, pi. xii. fig. 8. 



c c 4 



