BRITISH DESMIDIEiE. 65 



/3. (Ambleside specimen.) Length of joint, iwluding the connecting i)ro- 

 cesses, - ^ ^\ ^ ; length between foramina y^Vr 5 breadth of joint -^^. 



Tab. XXXII. f. 1 . c. portion of mature filament ; b, c, d. transverse views ; 

 e. portion of a filament of /3. (Ambleside specimen) ; /. portion of a filament 

 with dividing joints ; ff. two joints in an oblique position ; h. lateral view. 



5. SPH.EROZOSMA, Corda. 



Filament plane, fragile ; joints closely united by means of glandular 

 processes, and deeply divided on each side, thus forming two seg- 

 ments, and giving a pinnatifid appearance to the filament. 



The filaments are pale green, gelatinous, simple, plane, have a pin- 

 natifid appearance from the division of the joints into two segments, 

 are fragile, and finally separate into single joints. I have not 

 observed that the filaments are twisted, as in Desmidium and Didy- 

 moprium. At the junction of the joints there are on each margin one 

 or two minute glands or processes which are scarcely discernible in 

 the front view, and do not interfere with the close junction of the 

 joints. The transverse view is linear or oblong, and the processes, 

 one or two at each side, are much more evident than in the front 

 view. 



This genus differs from Desmidium, Didymoprium and Hyalotheca 

 in its flat filaments (which are not twisted), in the deep division of 

 the joints into segments, and especially in the presence of the minute 

 gland-like processes at the junction of the joints. 



On account of its deeply constricted joints, this genus forms a con- 

 necting link between the preceding and following genera. 



In Sphcerozosma, as in the other genera with deeply constricted 

 cells, the segments are frequently unequal during the growth of the 

 plant, and they become in like manner equal when it approaches 

 maturity, and its joints no longer divide. 



1. S. vertebratum (Breb.) ; joints as broad as long, deeply divided into 

 two segments by a narrow notch on each side. Junction-glands 

 oblique, solitary at the centre of each margin. 



Desmidium vertebratum, Breb. Alg. Fal. p. 65. t. 2. (1835). 



Sph(srozosma elegans, Corda, Ahnanach de Carlsbad, 1835, t. 4. fig. 37?; 



Observ. Micros, snr les Animal, de Carlsbad, p. 21. t. 4. f. 30? Hass. 



Br.Alff.p. 348. t. 84. f . 1. 

 Odontellal unidentata, Ehr. Infus. p. 159 (1838). 

 Isthmia vertebrata, Menegh. Synop. Desmicl. in Linncea 1840, p. 205. 

 Desmidium compressum, Ralfs, in Annals of Nat. Hist. v. 9. p. 253 (1842). 



