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



breadth, in close apposition with the lower half of the terminal 

 lobe. The two inner subdivisions are directed radially. The 

 outer is abruptly reflected towards the basal line of the segment, 

 and thus imparts the alate character for which the frond is so 

 conspicuous. The subdivisions of the lateral lobe, at first slightly 

 inflated, gradually taper to subacute apices, which, in like man- 

 ner with the apices of the terminal lobe, are tridentate. 



Length -0058"; breadth -0056". 



Lower Bengal, 1855. 



Plate XIII. fig. II. Front view. 



Lateral lobes inciso -dentate, or dichotomously incised. 



4. M. furcata, Ag. This species is very abundant, and occurs 

 in every state intermediate between the typical one and its 

 variety commonly described under the specific name of M. Crux- 

 melitensis. 



5. M. denticulata, Breb. 

 M. rot at a, Grev. 



These two forms are met with somewhat sparingly. As far 

 as I can judge, however, they present no character of sufficient 

 value to denote specific difference. The mere rounding off of 

 the dentate angles is surely too trifling a distinction to found 

 even a variety upon. The tendency to these slight modifications 

 in form has already been dwelt upon in describing the species 

 of Aptogonum. 



6. M. foliacea, Bailey. 



Var. ft. Fronds quadrangular, forming elongated filaments. 

 Segments 3-lobed. Lateral lobes dichotomously incised, with 

 a dentate process next the terminal lobe, which is dentato- 

 emarginate. 



Although the filamentous character of the Bengal form, and 

 the peculiar structure of its terminal lobe, do not tally with 

 the description given by Mr. Ealfs of M. foliacea, the occurrence 

 of the tooth-like projection next the terminal lobe, and the ge- 

 neral resemblance of the two forms, induce me to refer it to that 

 species. Indeed, judging from the very imperfect representation 

 of M . foliacea supplied to Mr. Ralfs by Prof. Bailey (British 

 Desmid. p. 210), it would appear probable that the minute 

 peculiarities of the one had in reality escaped observation in the 

 other. 



The characters of M. foliacea as given (loc. cit.) are as follows : 

 (( Frond subquadrate. End lobe narrow, with emarginate angles. 

 Lateral lobes inciso-dentate, with a short rounded tooth-like 



