BRITISH DESMIDIE^. 99 



Frond large, oval, twice as long as broad, deeply constricted at the middle ; 

 the apposition of the segments for their entire breadth renders the notch on 

 each side linear ; the pearly granules are large and confined to the margin, 

 where they form three to six series, the largest and central row producing 

 a dentate appearance ; the rest of the frond is merely punctate. 



The endochrome of each segment is often longitudinally di\'ided by a pale 

 line. The transverse \"iew is elliptic. 



Cosmarium ovale is one of the largest species in the genus ; its oval form 

 and its disc devoid of granules sufficiently characterise it. 



Length of frond yig of an inch ; breadth of segment -^-^ ; breadth of con- 

 nectmg portion y-^-g. 



Tab. XV. fig. 9. a. front view of empty frond ; b. side view. 



13. C. Botrytis (Bory) ; frond granulate, deeply constricted ; seg- 

 ments, in the front view, truncato-triangular ; end view elliptic. 



Heterocarpella Botrytis, Bory, Bid. Class, t. 8 (1825). 



Cosmarium deltoides, Corda, Aim. de Carlsh. 1835. p. 120. f. 18. 



Euastrum Botrytis, Ehr. Infus. p. 163 (1838). Kiitz. Phy. Germ. p. 136. 



Euastrum angulosum, Ehr. Infus. t. 10. f. 8 (1838). 



Cosmarium Botrytis, Meneghini, Synop. Desm. in Linncea 1840, p. 220. 



Ralfs, in Annals of Nat. Hist. v. 14. p. 393. t. 11. f. 5 ; Trans, of Bot. 



Soc. of Edinburgh, v, 2. p. 15. t. 16. Hassall, Brit. Alg. p. 363. 



Dolgelley and Penzance, /. B. Bristol, Mr. Thwaites. Bexhill, &c., 

 Sussex, 3/y. Jew/ie/*. Manchester; and Ambleside, ilfr. »S'/</e5oM«w«. Essex, 

 Mr. Hassall. Aberdeenshire, Dr. Dickie and 3Ir. P. Grant. Banffshire, 

 Mr. P. Grant. 



Germany, Ehrenberg. Falaise, Brebisson. 



Frond compressed, more or less rough mth pearly granules, which give a 

 denticulate appearance to the margui, deeply constricted at the middle, the 

 constriction forming a hnear notch on each side. In the front view the seg- 

 ments are broadest at the base and gradually narrower towards the end, which 

 is trmicated ; hence their figure is somewhat angidar. The transverse view is 

 elliptic. 



The pearly granules are sometimes very evident, sometimes obscure, but 

 they can always be detected at the margin by the higher powers of the mi- 

 croscope. 



Mr. Thwaites has gathered a single sporangium near Bristol ; it was orbi- 

 cular, its spines elongated and slightly divided at the apex. 



Cosmarium Botrytis may be known from C. margaritiferum by its trmicate 

 ends ; and from C. pyramidatutn by its more triangular segments and denti- 

 cidate margins. 



Length of frond from -^ to 3-L5- of an inch ; breadth at constriction 2-5V0 

 to y^Vb" ' hreadth of segment -^\-g to j^^ ; diameter of sporangium -g^ ; 

 length of spines of sporangium y^Vr* 



Tab. XVI. fig. 1. a. mature frond; b. empty frond; c. transverse view; 

 d. sporangium with empty fronds attached. 



H 



