BRITISH DESMIDIE.ii. 151 



Closterium Digitus, Ehr. Abfi. der BerL Jk. (1831), p. 68 ; Infas. p. 94. 



t. 6. f . 3 ? Meneghini, Sijnop. Desmid. itiLinncea 1840, p. 230. Bailey, 



Amer. Bad/, in Amer. Journ. of Science and Arts, v. 4 1 . p. 302. 1. 1 . f. 33. 



Jenner, Fl. of Tunhridye Wells, p. 196. Hassall, Brit. Ahj. p. 370. 



Kiitzing, Bhy. Germ. p. 132. 

 Closterium lamellosum, Brebisson, Aly. Fat. p. 59. t. 8 (1835). 

 Pleurosici/os myriojiodus, Corda, Aim. de Carlsb. 1835, p. 125. t. 5. f. 68. 

 Penium Digit as, Brebisson, in lit. (1847). 

 Polysolenia Closterium, Ehr. MS. Baile}", in lit. 



Very common. Wales and Penzance, J. R. Sussex, Surrey, Kent and 

 Hants, Mr. Jenner. Kerry, Mr. Andrews. Near Bristol, 3Ir. Thwaites. 

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

 Ambleside, Mr. Sidebotham. 



Germany, Ehrenberg, Kiitzing, Corda. Falaise, Brebisson. Maine to 

 Virginia, Bailey. 



Frond smooth, stout, three to five times longer than broad, elliptic or ellip- 

 tic-oblong ; not unfrequently however the frond is dilated at one end and 

 becomes ovato-oblong ; the ends are broadly rounded. The endochrome is 

 yellow-green with a pale transverse band at the middle ; there are no regular 

 fillets, but longitudinal undulations are more or less perceptible. Terminal 

 globules wanting, or very indistinct, in British specimens. The end view is 

 circular, and the endochrome radiate. The empty frond is colourless, flexible, 

 and without markings. 



Ehrenberg' s description and figure of his Closterium Digitus is unlike the 

 plant here described, and Brebisson formerly supposed it was intended for the 

 next species ; but the whole outline and the description of the rounded ends 

 are certainly more suital)le to this. I have never seen any terminal vesicles, 

 yet they are depicted by Ehrenberg and also by Professor Bailey in a figure 

 in his 'American Bacillaria.' 



In the recent state there can be no danger of confounding Penivm Digitus 

 with P. interruptum ; and even in the dried state, although the conspicuous 

 differences dependent on the disposition of the endochrome are no longer to be 

 found, the form of the frond appears to me a sufficient distinction. 



Length of frond -^ of an inch ; greatest breadth -^^. 



Tab. XXV. fig. 3. a, b. fronds with endochrome ; c. empty frond. 



4. P. interruptum (Breb.) ; frond smooth, cylindrical; extremities 

 conical with rounded apex ; fillets strongly marked, interrupted by 

 three transverse bands. 



Penium interruptum, Brebisson, hi lit. (1846). 



Dolgelley and Penzance, J. R. Ashdown Forest and Chiltington Common, 

 Sussex, 3Ir. Jenner. Ambleside, "Westmoreland, Mr. Sidebotham. 



Falaise, Brebisson. 



Frond stout, four to six times longer than broad, quite straight, cylindrical, 

 so that the sides are parallel, except at the extremities, which are rather sud- 

 denly conical and rounded at the apex. Endochrome dark green ; fillets 

 straight, three or four strongly marked and a fainter one near each margin. 



