390 DESMIDEiE. 



crasterias Boryana Ehr., Infus. p. 157. pi. f. 5. a. c. x. 

 k, h, 1, fj g, but not b, c, d, e. Micrasterias tricyclia 

 Ehr., Infus. p. 158. pi. xi. f. 8. b, c, cl, f, g, e, i, but 

 not a. Pediastrum Boryanum Menegh., Synops. Desmid. 

 p. 210.; Bailey, American Bacil. fig. 20. Pediastrum 

 Boryanum Ralfs, in Annals, vol. xiv. p. 470. pi. xii. 

 fig. 7. in part 1. 



Hab. Cheshunt, Herts : A. H. H. Brambletye, near 

 Forest Row ; Tunbridge Wells, &c. : Mr. Jenner. Dol- 

 gelley ; Barmouth ; and Penzance : Mr. Ralfs. 



It appears to me that more than one species has been con- 

 founded together by different observers, and regarded as the 

 present plant. Ehrenberg has figured four species under 

 the name of Micrasterias Boryana, one of these being re- 

 ferrible to the Micrasterias tricyclia of Ehrenberg, pi. xi. 

 fig. 7. a, a plant which is British, and Mr. Ralfs, pro- 

 bably three species, the one of these being doubtless identical 

 with Ehrenberg's Micrasterias angulosa. The Pediastrum 

 Boryanum is the commonest species of the genus. 



" Sometimes plants are met with having more than three 

 circles : these are probably the Micrasterias elliptica Ehr., 

 Infus. p. 158. tab. xi. fig. 9., which Meneghini refers to 

 the present species. I am not, however, satisfied that it is 

 not distinct : the external cells agree with the description 

 given above, but the inner ones are variable in number, and 

 not arranged in regular circles. Whether it possesses any 

 other distinctive character I have not yet clearly ascertained. 

 This form is fig. 21. of the American * Bacillaria.' " — Ralfs. 



5. Pediastrum tricyclium Hass. 



Plate XCII. Fig. 1. 



Char. Fronds usually constituted of three circles, the inner 

 circle formed of four or five cells placed round a central 

 cell, the second circle of eight or ten cells, and the third 

 circle of fifteen cells. Cells somewhat quadriform, those of 

 the centre as well as the marginal ones usually incised. 



