278 Dr. G. C. Wallich on Desmidiacea from Lower Bengal, 



differences are permitted to exercise an undue weight, we shall 

 never be able to disencumber our lists of the multitude of ficti- 

 tious species they contain. I would particularly draw attention 

 to the manner in which species have been extended in the genus 

 I am now discussing, upon the slender basis of a notch or a 

 tooth more or less ; whereas, in some of the figures of the same 

 species, and, in some cases, actually in the two segments of the 

 same frond, differences quite as great or greater are visible. As 

 it at present stands, the genus Micrasterias numbers upwards of 

 twenty species, which I firmly believe are reducible to less than 

 half that number, without infringing on a single reliable distinc- 

 tive character. 



In the figures of M. morsa given by Mr. llalfs, as also in that 

 given by Professor Bailey, to which allusion has been made, and 

 which was referred to as an Euastrum, the extremities of the 

 furcate terminal lobe are made to appear bifid. Mr. llalfs' s 

 description, moreover, would show that such was his view of its 

 structure. It may be somewhat rash in me to offer an opinion 

 as to the bifid appearance being due to the compression of the fur- 

 cate processes, which have been described as being placed at right 

 angles to the plane of the frond. Nevertheless, having repeatedly 

 seen the same appearance presented, and having always been 

 able, by careful adjustment of the microscope, to trace these pro- 

 cesses to their independent base, I venture to believe that the 

 structure is the same in each of these forms. In one of Mr. 

 Ralfs's figures of M. . morsa, the true character is actually given 

 in one half of the terminal lobe, whilst it is not so in the other. 



Mr. llalfs states that " M. morsa differs from M. Crux-meli- 

 tensis in the bifid angles of the end lobes, and in the concave 

 and serrated margin, as well as the less divided state of the 

 lateral lobes." But the same author gives the characters of M. 

 Crux-metitensis as follows : " Frond rotundato-elliptic ; segments 

 sub-five-lobed ; lobes bifid, subdivisions short and bidentate at 

 the apex," and adds that the frond is about the same size as 

 that of M. furcata, and similarly divided, but the incisions are less 

 deep, the subdivisions stouter and less divergent, and their ex- 

 tremities are rather bidentate than forked. In HassalFs ( Fresh- 

 water Algae/ p. 387, it is stated that the frond of the true M. 

 Crux-melitensis is oval rather than circular, and each segment is 

 three-lobed instead of five-, and the lobes themselves are not 

 approximate, but divergent. As figured by Mr. Ralfs, M. Crux- 

 melitensis is quite distinct from this form, the frond being, more- 

 over, perfectly smooth ; whereas the figure of M. morsa shows 

 that its structure is punctate or granular. For M. Baileyi the 

 characters given by Mr. llalfs are : " Frond granulated ; seg- 

 ments 3-lobed ; lobes bipartite, end one much exserted." " M. 

 Baileyi is allied to M. furcata and M, Crux-melitensis ', the 



