100 BRITISH DESMIDIE^. 



14. C. margaritiferum (Turp.) ; frond rough with pearly granules, 

 which are as broad as long ; segments semiorbicular or reniform ; 

 end view elliptic. 



«. Segments semiorbicular. 



/3. reniformis ; segments reniform. 



TJrsinella margaritifera, Turp. Diet, des Sc. Nat. f. 23 (1820) ; Mem. du 



Mus. p. 295. t. 13. f. 19. 

 Cymhella reniformis, Ag. Consp. Diatom, p. 10 (1830). Leibl. Fl. 1830, 



p. 315. t. 1. f. 2. Greville, in Hook. Br. Fl. v. 2. p. 415. Harvey, 



Brit. Alg. p. 215. 

 HeterocarpeUa Ursinella, Kiitziiig, Synop. Diatom, in Linncea 1833, p. 598. 

 Euastrum margaritiferum, Ehr. Ahh. der Berl. Ak. 1833, p. 246 ; Infus. 



p. 163. t. 12. f. 7. Kiitzing, Phycol. Germ. p. 136. Bailey, Amer. 



Jovrn. of Science and Arts, v. 41. p. 295. f. 8. 

 Micrasterias margaritifera, Brebisson, Alg. Fal. p. 55. t. 7 (1835). 

 Cosmarium margaritiferum, Meneghini, Synop. Desmid. in Linncea 1840, 



p. 219. Ralfs, in Annals of Nat. Hist. v. 14. p. 393. t. 11. f. 4; 



Trans, of Bot. Soc. of Edinburgh, v. 2. p. 15. t. 16. 



Very common. Dolgelley ; Carnarvon; near Carmarthen ; Penzance, &c., 

 J. R. Barmouth, Rev. T. Salwey. Sussex ; Kent ; Surrey ; and Weston 

 Bogs near Southampton, Mr. Je^iner. Farnham, Surrey, Mr. Reeves. Herts, 

 Mr. Hassall. Near Bristol, Mr. Thwaites and Mr. Broome. Kerry, Mr. 

 Andrews. Near Manchester, Mr. Gray. Cheshire and Westmoreland, Mr. 

 Sidebotham. Aberdeenshire and Banffshire, Dr. Dickie and Mr. P. Grant. 

 Rochdale, Mr. Coates. 



Germany, Leiblein, Ehrenberg and Kixtzing. Falaise, Brebisson. West 

 Point, New York ; and in Mexico, Bailey. 



Frond compressed, deeply constricted at the middle, the constriction causing 

 a linear notch on each side. The segments are broader than long, semiorbi- 

 cular or reniform, and rough with pearly granules, which are as broad as long, 

 and give a dentate appearance to the outline. The transverse view is elliptic. 



The sporangia of this species, which I have gathered at Dolgelley, are or- 

 bicular and inclosed in a granulate cell, which is usually somewhat angular. 



Cosmarium margaritiferum varies in size and form. The rough frond 

 distinguishes it from C. crenatum and C. undulatnm ; its rounded ends from 

 C. Botrytis ; its smaller size and shorter granules from C Brebissonii, and its 

 less angular shape from C. conspersum. 



Length of frond from -g^ to -3^^ of an inch ; breadth from -^^ to ^J-g- ; 

 diameter of sporangium -g\j ; length of spines of the sporangium 2-2^ ; length 

 of swollen base of spine x^Vf 



Tab. XVI. fig. 2. a. var. /3 ; h. empty frond of a ; c. transverse view j 

 d. sporangium with empty segments of conjugated fronds. Tab. XXXIII. 

 fig. 3. a,b. mature sporangia. 



15. C. Brebissonii (Menegh.) ; frond rough with conic spines or 

 granules ; segments semiorbicular ; end view elliptic. 



Cosmarium Brebissonii, Meneghini, Synop. Desmid. in Linncea 1840, p. 219. 



