Dr. G. C. Wallich on Desmidiacea from Lower Bengal 193 



5. Leuronema, n. g. 



filament compressed or triangular. Margins incised or 

 sinuate. Joints deeply constricted. Without intermediate 

 processes. 



The absence of intermediate processes of any kind whatso- 

 ever renders it necessary to separate the following forms from 

 Spharozosma, in which genus the connecting tubercles consti- 

 tute a primary character. Three varieties occur abundantly in 

 some gatherings, but neither of these exhibits the slightest trace 

 of intermediate processes under any circumstances. The joints 

 seem merely to be pressed together, edge to edge, and to be 

 retained in position by the general mucous envelope common, 

 in greater or less degree, to all the filamentous Desmidiacea3 of 

 Lower Bengal, and to the majority of the non-filamentous forms. 

 It can scarcely be doubted that this envelope is universal, 

 although less easily seen in a few species. 



The filaments are of great length, notwithstanding the absence 

 of any special uniting processes, and do not break up more 

 readily into single joints than their allied forms. A single joint 

 of the compressed species, when separate, might readily be mis- 

 taken for a small Cosmarium -, whilst one of the triangular 

 variety might in like manner be looked upon as a Staurastrum. 

 But the strictly filamentous character shared by both serves at 

 once to distinguish them from both of these genera. 



I have numerous specimens of the compressed species which 

 exhibit spherical sporangium-like bodies, attached at one point 

 to the constricted base of the joints ; but there is no evidence 

 forthcoming to prove that these bodies are the product of con- 

 jugation of pairs of joints from different filaments, as is the case 

 in the sporangial state of the species already described by me. 

 They may be perfect sporangia, however, if we conceive the 

 second series of conjugated joints to have separated, or to have 

 broken up, on the completion of their functions. However this 

 may be, the cysts containing the bodies in question spring from 

 precisely the same point as in the other forms noted namely, 

 from the base of the constriction ; and it is therefore difficult to 

 consider them in any other light than as sporangia. If admitted 

 to be such, their smooth, plane cell-wall affords a strong addi- 

 tional ground of distinction from Cosmarium and Staurastrum 

 respectively. 



1. L. nitens, n. s. Filament pinnatifid. Joints compressed, 

 deeply constricted. Extremities of joints rounded. 



The connecting surfaces of the joints in this form are quite 

 plane, and the segments are closely approximated. Joints 



