BRITISH DESMIDIE.E. 153 



they are orbicular and situated between the conjugating fronds, from which, 

 after their formation, they soon become detached, 



Penium tnmcatum closely resembles a small specimen of P. Brehissonii, but 

 it is much smaller and its ends are truncate. In form it agrees with P. Cylin- 

 drus, but in that species the empty frond is coloured and distinctly granulate. 



Length of frond from g^ to -^\-g of an inch ; breadth from 2-2V2 *« -oT^o^ 5 

 diameter of sporangium -^\^. 



Tab, XXV. fig, 5. a, b, c. mature fronds ; d. dividing frond ; e. conjugated 

 fronds ; f, g. sporangia. 



7. P. Jenneri ; fi'ond smooth, cylindrical with rounded ends ; 



sporangium orbicular, situated between the conjugating fronds, 

 which are deciduous. 



Bogs at Fisher's Castle, Tmib ridge Wells, Mr. Jetiner. 



Frond variable in length, from two to four times longer than broad, oblong 

 or cylindrical with rounded ends, 



I know no character by which to distinguish the usual state of Penmm Jen- 

 neri from P, Brebissonii. They agree in size and form ; in both the arrange- 

 ment of the endochrome is similar, and the transverse pale band at the mid- 

 dle is often indistinct ; the empty frond also is smooth and colourless, and 

 no suture can be detected. Still the diiferent fonns of their sporangia compel 

 us to consider them as distinct species. 



In the present plant the conjugating fronds do not open and gape at the 

 suture, as is usual in the Desmidiese, but couple by small and distinct cylin- 

 drical tubes, like many in the Conjugatee. The sporangium is orbicular, and 

 situated between the fronds, withhi the dilated connecting tube. 



The frond in Penium Jenneri is more rounded at its ends and larger than 

 those of P, truncatum ; in the latter species, moreover, the conjugating cells 

 gape at the suture ; in both they are but slightly attached to the sporangium. 



Length of frond from -^^ to ^3^ of an inch ; breadth from i^^Vt ^^ tbW 5 

 diameter of sporangium x^o^- 



Tab, XXXIII, fig. 2, a, b, e, e. fronds with endochrome ; d. empty frond ; 

 f. dividing frond ; g. conjugated fronds ; h, i. mature sporangia, 



tt Sporangium permanently attached to the conjugated cells, at first 

 quadrate, then orbicular (Cylindrocystis). 



8. P. Brebissonii (Menegh.) ; frond smooth, cylindrical with rounded 

 ends, transverse central band inconspicuous ; sporangium at first 

 quadrate but finally orbicular ; conjugating fronds persistent. 



Palmella cylindrospora, Brebisson, Alg. Fal. p. 64 (1835). 



Cylindrocystis Brebissonii, Meneghini, Cenni suUa organografia e fisiol. delle 

 Alg. pp. 5, 26 (1838) ; Monog. Nost. t. 12. f. 3. Hassall, Brit. Fresh- 

 water Alg. p, 361. t. 92. f. 17. 



Cymbella? Icetevirens, Harvey, Man. of Brit. Alg. p. 216 (1841). 



Closterium Cylindrocystis, Kiitzing, Phy. Germ. p. 132 (1845). 



