196 Dr. G. C. Wallich on Desmidiacea from Lower Bengal. 



7. Streptonema, n. g. 



Filament interrupted. Triangular, deeply pinnatifid. Joints 

 deeply constricted, and united to each other by three cylindrical 

 hyaline bands given off from the base of each lobe. Segments 

 deeply 3-lobed. 



1. S. trilolatum, n. s. Joints very deeply constricted, furnished 

 on their outer surfaces with three stout connecting bands, 

 which unite with those from the adjacent joints. Segments 

 3-lobed ; bases of lobes parallel with the base of constriction. 



This genus is allied to Sphcerozosma ; but the structure of the 

 connecting processes is so unique as to leave no doubt of its 

 distinct character. Seen in the front view, under the micro- 

 scope, the filament looks somewhat less symmetrical in the 

 disposition of its details than is usual in the beautiful class of 

 organisms to which it belongs ; but this want of perfect sym- 

 metry is due to causes that do not affect it in its normal condi- 

 tion. Thus seen, the lobes are distorted to some extent, and the 

 connecting bands, in like manner, appear less direct than they 

 ought to do. This form is nevertheless peculiarly elegant. 



The constricted portion of the joints presents a short isthmus. 

 The segments are accordingly not very closely approximated. 

 Each lobe is inflated towards its free extremity. In the end 

 view the joints are triradiate ; the central isthmus appearing as 

 a circular cavity, from the margin of which the lobes arise at 

 equal distances, and the tubercular bases of the connecting 

 bands being placed midway between them. 



The connecting processes or bands are marked by three trans- 

 verse lines, at the central one of which the bands are somewhat 

 thickened. When the filament breaks up, the bands disunite at 

 either of these lines ; and, at first sight, it would appear as if 

 each band were formed by the interposition of two short cylinders 

 attached to the projecting tubercles situated, as already described, 

 at the base of each lobe. 



Whilst the joints are undergoing division, the young segments 

 are closely pressed together, and the rudiments of the connecting 

 bands are to be seen in the form of minute flattened processes, 

 which gradually extend outwards as the two new joints become 

 perfect and separate, and ultimately constitute the connecting 

 bands. 



The sporangium is formed by the conjugation of the joints of 

 two distinct filaments, as described in Desmidium andAptogonum, 

 a sac-like vesicle being protruded from the base of the opposed 

 joints, these vesicles by degrees coalescing to form a cell, into 

 which the endochrome is collected. Before the sporangial mass 

 is quite mature, the filament breaks up ; but several of the spo- 



