144 W. B. TURNER, FRESH-WATER ALGJE OF EAST INDIA. 



Typ. sp. S. Wallichii. 



C. Oxyzosma (o£vg, acer; &c). Latera 1 margins acute-angled. 



Typ. sp. S. Indicum, n. sp.; No. 4 supra. 



Gen. 23. Streptonema, Wallich. 



(Desm. Beng. p. 190, 1860; Trigonema, Wallich Mscr. 1855). Fila interrupta, triangularia, profunde pinna 

 titida; frondes profunde constrictse, vittis tribus cylindraceia hyalinis e basi loböruin evadentibus eonjunetae. 



Semicellulae profunde t.rilobat;e. G. C. AV. 1. c. 



1. Str. trilobatum, Wallich (1. c. Desm. Beng. t. VIII, f. 1 — 6, 1860; Trigonema trilo- 

 batum, Wall. Mscr. 39— 4b\ 1855). 



»Joints very deeply constricted, furnished on their outer surfäces with 3 stout 

 eonnecting bands, which unite with those from the adjacent joints. Segments 3-löbed; 

 bases of lobes parallel with the base of eonstriction.» 



»This genus is allied to Sphcerozosma: hut the structure of the eonnecting pro- 

 cesses is so unique as to leave no doubt of its distinct chäractér. Seen in the front 

 view, under the microscope . . . the lobes are distorted to some extent, and the eon- 

 necting bands, in like tnanner, appear less direct tlian they ought to do.» 



The constricted portion of the joints presents a short isthmus. The segments 

 are accordingly not very eloselv appröximated. 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 eonnecting bands being placed midway between them.» 



»The eonnecting processes or bands are marked by three transverse lines, at the 

 central one of which the bands are somewhat thickened. Wlien the filament breaks 

 up, the bands disunite at either of these lines; and, at tirst sight, it would appear as 

 if each band were forined by the interposition of two short cylinders attached to the 

 projeeting tubercles situated, as already described, at the base of each lobe.» 



»Whilst the joints are nndergoing division, the young segments are closely 

 pressed together, and the rucliments of the eonnecting bands are to be seen in the form 

 of minute nattened processes, which gradually extend outwards as the two new joints 

 become perfect and separate, and ultimately constitute the eonnecting bands.» 



»The sporangium is formed by the conjugation of the joints of two distinct fila- 

 ments, as described in Desmidium and Aptogonum — a sac-like vesiele being pro- 

 tnded from the base of the opposed joints, these vesicles by degrees eoalescing to form 

 a cell, into which the endochrome is collected. Before the sporangial mäss is quite 

 mature, the filament breaks up; but several of the sporangial sacs, with their parent- 

 joints still attached, are constantly to be met with, placed side by side, and probably 

 retained near each other by a common mucous envelope. The cells at this period are 

 elliptical, their ends being produced somewhat, and eoalescing with the iioav empty 

 joints. At maturity, the old joints are cast off entirely, the cell closes, assumes a 

 perfectly elliptical outline, and the sporangium presents itself in a guise similar to 

 the mature detached Sporangia seen in some of the Zygnemaceaa,» Wallich, Desm. 

 Beng. pp. 196 — 7. Xo distinct mucous sheath! 



