BRITISH DESMIDIE.E. I7I 



p. 95. t. 6. f. 12. Meneghini, Spiopsis Desmid: inLinnaiu 1840, p. 234. 

 Bailey, Amer. Journ. of Science and Arts, v. 41. p. 303. t. 1. f. 35. 

 Kiitzing, Phycologia Gennanica, p. 131. Jenner, Fl. of Tunbridye 

 JJ'elis, p. 196. Ilassall, Brit. Freshwater Algce, p. 3/3. 



Common. Carnarvon ; Dolgelley ; Tal Sam near Lampeter ; near Car- 

 marthen ; and Penzance, /. R. Sussex ; Surrey ; Kent ; and Hampshire, 

 Mr. Jenner. Kerry, Mr. Andrews. Galway, Mr. M'Calla. Hertfordshire, 

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

 Westmoreland, Mr. Sidebotham. Manchester, Mr. Gray and Mr. Wil- 

 lianiso?i. 



Germany, Ehrenberg. New York ; and New England, Bailey. Falaise, 

 Brebisson. 



Frond six to twelve times longer than broad, very variable in both length 

 and breadth, curv^ed, tapering from the middle ; ends very obtuse ; upper 

 margin convex ; lower concave or straight, but never inclined upwards at the 

 ends. Vesicles in a single series ; fillets often obscure. This species forms 

 yellomsh-brown masses in the water. 



The empty frond is reddish and darkest at the ends. Striae numerous, 

 crowded, and easily detected. Sutures usually three, but sometimes only two : 

 specimens with a single suture are very rare. 



The sporangia, which are not macommonly met with, are orbicular and placed 

 between the deciduous fronds. 



Closterium striolatum is shorter than C. turgidum, and the ends do not turn 

 up ; its striae are much more numerous and close than those of C. costatum ; 

 and both C. turgiduni and C. costatum have constantly but a single suture. 

 It is more closely striated than either C. intermedium or C. angustatum, and 

 stouter also in proportion to its length. With this species C. didymotocum 

 in some respects agrees as to its size and form, but it is straighter and less 

 tapering, and its ends are more truncate, and the strise, if present, are detected 

 with the greatest difficulty. 



Length of frond from ^^ to ^L of an inch ; greatest breadth from -g-L- to 

 •g-L ; distance between the strise y^.oTo. 



Tab. XXIX. fig. 2. a,b, c. fronds with eudochrome ; d, e,f. empty fronds ; 

 g, h. sporangia. 



14. C. intermedium ; frond slender, slightly curved, tapering ; 



striae distinct, not crowded ; sutures usually more than three. 

 Dolgelley, J. R. 



Frond slender, nearly straight, many times longer than broad, very gradu- 

 ally tapering, ends truncate. Fillets obscure ; vesicles in a single series. This 

 species forms in the water large masses of a yellow-brown colour. 



The empty frond is straw-colour ; its strise are distinct and can be counted 

 without difficulty. Sutures, though occasionally but three, are usually from 

 four to seven in number. The central suture often forms a pellucid line re- 

 sembling a dissepiment. 



In its form and in the number of its striee Closterium intermedium is inter- 

 mediate between C. striolatum and C. angustatum. According to M. de Bre- 

 bisson, 6'. striolatum has about forty strise, C. intermedium twenty, and C. an- 



