170 BRITISH DESMIDIEiS. 



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 

 ends, transverse suture distinct. Longitudinal striae numerous, close, gene- 

 rally faint, but sometimes very distinct. 



Closterium attenxmtxim 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 inch ; greatest breadth -^^ ; distance between the 



®^^l^ 26315* 



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



1 2. C costatum (Corda) ; frond stout, semilunate or crescent-shaped, 

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

 suture solitary. 



Closterium costahim, Corda, Almanack de Carlshad, 1835, p. 124. t. 5. f. 61 

 to 63 ; Observations microscopiques sur les Animalcules desEanx et des 

 Thei'mes de Carlsbad, p. 34. Brebisson, in lit. cum icone. 



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

 1840, p. 237. 



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

 cum icone. 



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

 JeJiner. 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 suture generally of 

 two or more lines. The longitudinal striae, 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 

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

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

 than theirs. 



Length of frond yL of an inch ; greatest breadth gJ^ ; distance of striae 



^P^^^ 5 3 19* 



Tab. XXIX. fig. 1. 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 striohduw, Ehrenberg, Abh. der Berlin. Ak. 1833, p. 68 ; Infusor. 



