170 BRITISH DESMIDIE^. 



times longer than broad, curved, gradually attenuated, and at the end suddenly 

 contracted into an obtuse, conical or subcylindrical point. Fillets obscure ; 

 vesicles in a single longitudinal series. Empty frond reddish, especially at the 

 end?, transverse suture distinct. Longitudinal strise numerous, close, gene- 

 rally faint, but sometimes very distinct. 



Closterium attenuatum might be supposed an incomplete state of another 

 species, especially when its ends are dissimilar ; but the sudden contraction of 

 the extremities is a sufficient distinction. 



Length of frond -^ of an uich ; greatest breadth -^ ; distance between the 



stnae 2631 s* 



Tab. XXIX. fig. 5. a. frond with endochrome ; h. empty frond. 



12, C. cosfatum (Corda) ; frond stout, semilunate or crescent-shaped, 

 tapering from the middle ; ends obtuse ; striae few and conspicuous ; 

 suture solitary. 



Closterium costatum, Corda, Almanach de Carlsbad, 1835, p. 124. t. 5. f. 61 

 to 63 ; Observations microscopiques sur les Animalcules desEaux et des 

 Thermes de Carlsbad, p. 34. Brebisson, in lit. cum icone. 



Closterium doliolatum, Brebisson, Meneghini, Synopsis Besmid. in Linncea 

 1840, p. 237. 



Closterium dilatatum, Kiitzing, Phycologia Germanica, p. 132 (1845) ; in lit. 

 cum icone. 



Dolgelley ; and Penzance, /. R. Sussex ; Surrey ; and Hampshire, Mr. 

 Jenner. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. 

 Sidebotham. Near Bristol, Mr. Broome. 



Carlsbad ; and Prague, Corda. Falaise, Brebisson. 



Frond stout, five or six times longer than broad, crescent-shaped or nearly 

 semilunate, rapidly attenuated from the centre ; end obtuse or somewhat trun- 

 cate. Fillets obscure ; vesicles in a single series. 



The empty frond is reddish, with a single transverse sutiAe generally of 

 two or more lines. The longitudinal strise, which are few compared to the 

 breadth of the frond, are so very distinct that they may be counted without 

 difficulty. 



I have gathered a single sporangium at Dolgelley ; it was orbicular, and 

 resembled that of Closterium striolatum. 



This species agrees with Closterium angustatum in its distinct, subdistant 

 strise ; but their forms are widely different. It is stouter in proportion to its 

 length than either C. turgidum or C. striolatum, and its strise are much fewer 

 than theirs. 



Length of frond -^-^ of an inch ; greatest breadth -^^^ ; distance of strise 

 apart -j^. 



Tab. XXIX. fig. I. a. frond with endochrome; b. empty frond. 



13. C. striolatum (Ehr.) ; frond closely but distinctly striated, semi- 

 lunate or crescent-shaped, tapering from the middle ; sutures gene- 

 rally three, never more. 



Closterium striolatum, Ehrenberg, Abh. der Berlin. Ah. 1833, p. 68 ; Infusor. 



