Mr. J. Ralfs on the British Desmidiese. 393 



somewhat cruciform. The surface is rough with pearly granules, 

 which give a dentate appearance to the margin. 



In the front view this species closely resembles C. margariti- 

 ferum, and frequently can scarcely be distinguished from it, but 

 the end is straight, not rounded in the middle, and in general 

 slightly projects. In the end view they are very different. 



Plate XI. fig. 3. C. ornatum : a, front view; b, empty frond; c, c, end 

 views. 



4. C. margaritiferum, Mgh. Fronds rough with pearly granules, 

 deeply constricted, the constriction forming a linear notch on each 

 side ; segments compressed ; end view elliptic. Menegh. Synop. 

 Desmid. in Linnaea 1840, p. 219. Cosmarium dentiferum, Corda, 

 Obser. microscop. sur les Animalc. de Carlsbad, p. 30. pi. 6. fig. 41 . 

 Euastrum margaritiferum, Ehr. Infus. p. 163. tab. 12. fig. 7; Pritch. 

 Infus. p. 196. fig. 126; Bailey, Amer. Bacil. in Am. Journ. of Sci- 

 ences and Arts, vol. xli. no. 2. p. 295. fig. 8. Ursinella margari- 

 tifera, Turp. Diet, des Sc. Nat. par Leur. Atl. Veg. (1820.) He- 

 terocarpella Ursinella, Kutz. Syn. Diatom, p. 598. Cymbella rent- 



formis, Ag. Consp. Diatom, p. 10; Grev. in Hook. Br. Fl. vol. ii. 



p. 415 ; Harv. Br. Alg. p. 215. 



In bogs, pools, &c, probably common. Weston Bogs near South- 

 ampton, and numerous habitats in Sussex and Kent, Mr. Jenner ; 

 Farnham, Surrey, Mr. Reeves ; Cheshunt, Herts, Mr. Hassall ; near 

 Bristol, Mr. Thwaites; Barmouth, Rev. T. Salwey ; Dolgelley, Caer- 

 narvon and Penzance. 



Fronds rough with pearly granules, deeply constricted in the 

 middle ; the segments in close apposition for their entire breadth, 

 whence the constriction appears like a linear notch on each side. 

 The segments are broader than long, subreniform, compressed. 

 The end view is elliptic. 



This species is very variable in the size, form, and number of 

 the granules on the surface. Mr. Jenner has sent me drawings 

 of some plants which I am compelled at present to refer to this 

 species, but it is very probable that a better knowledge of them 

 will discover characters by which they may be distinguished from 

 it. In general the granules are of considerable size and give a 

 dentate appearance to the margin, but in some specimens the 

 margin appears quite entire ; sometimes they are obtuse, at others 

 acute. 



Plate XI. fig. 4. C. margaritiferum : a, a, front views; b, new segments ; 

 c, empty frond of a variety with entire margins; d, side view ; e, end view. 



5. C. Botrytis, Mgh. Fronds granulated, compressed, deeply con- 

 stricted, the constriction forming a linear notch on each side; the 

 segments in the front view are truncato-triangular ; end view 

 elliptic. Menegh. /. c. p. 220. Euastrum Botrytis, Ehr. Infus. 

 p. 163. tab. 10. fig. 8. 



In pools. Near Bristol, Mr. Thwaites ; Sussex, Mr. Jenner; near 

 Manchester, Mr. Sidebotham ; Dolgelley. 



