14 Mr. J. Ralfs on the British Desmidiez. 
have not observed that the filaments are twisted, as in Desmidium 
and Didymoprium. » At the junction of the jomts 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 im the front view. 
: This genus differs from Desmidium, Didymoprium and Gileo- 
prium in its flat filaments (which are not twisted), in the deep di- 
vision of the joints into segments, and especially in the presence 
of the minute gland-like processes at the junction of the joints. 
From the Odontella of Ehrenberg it may be known by the joimts 
being united along their entire breadth, whereas in Odontella they 
are connected only by the elongated angles which inclose a small 
vacant space between them. 
On account of its deeply constricted joints, this genus forms a 
connecting link between the three preceding genera and Stau- 
rastrum. 
In Spherozosma, as in the other genera with deeply constricted 
cells, the segments are frequently unequal durmg the growth of 
the plant, and they become in like manner equal when it ap- 
proaches maturity and its joints no longer divide. 
1. S. unidentata. Jointsas broad as long, divided into two segments 
by a linear notch on each side ; junction-glands stalked, oblique, 
solitary at the centre of each margin. Odontella unidentata, Ehr. 
Infus. p. 159; Pritch. Infus. p.191. Desmidium compressum, An- 
nals of Nat. Hist. vol. ix. p. 253. Isthmia vertebrata, Menegh. 1. c. 
p. 205 ? . 
This plant has been gathered at Rotherfield and near Tun- 
bridge Wells by Mr. Jenner since the publication of my former 
notice of it. I then considered it an undescribed species of Des- 
midium. 1 have since been favoured by Mr. Berkeley with the 
following extract from Ehrenberg’s observations on the Odon- 
tella unidentata :—“ This species is surprismg by reason of its 
evolution. There are always two great and two small joints 
alternately turned to one another, and the processes are found 
alternately between the small and large jomts. This reminds one 
of Scenedesmus convergens and the Euastra.” This extract leaves 
no doubt that Ehrenberg’s Odontella unidentata is identical with 
the plant I described under the name of Desmidium compressum. 
He correctly pomts out the affinity between the jomts in this 
plant and the frond in Euastrum. As in both genera he consi- 
ders the segments of the cell to be distinct joints, he has de- 
scribed the process or junction-gland in the present plant as oc- 
curring at every alternate dissepiment. But his description of the 
