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



but is unquestionably a small variety of the species described by 

 Kiitzing as Euastrum incisum (Phyc. Germ. p. 134), and pro- 

 perly belongs to the present genus. 



Micrasterias quadrata, Bailey (' Smithsonian Contrib., Microsc. 

 Observ. in South Carolina, &c/), appears to be merely a large 

 variety of M. oscitans, Ralfs. 



Length -0021"; breadth -0021". 



Lower Bengal. 



Plate XIII. fig. 1. Front view. Figs. 2 & 3, showing the development 

 of the terminal lobe. 



2. H. incisa, Kiitz. Lobes divided by a deep incision. Basal lobe 



linear or slightly sinuate, truncate; its extremities emar- 



ginate; both angles furnished with a mucro. Terminal lobe 



fusiform, mucronate. 



Micrasterias incisa, Kiitz. 



This species differs from H. oscitans in having abruptly trun- 

 cate, linear basal lobes; in the latter being emarginate, and 

 having both angles mucronate. The frond is quadrilateral, the 

 terminal lobe being nearly as long, but not so large and turgid, 

 as the basal one. The constriction between the segments and 

 lobes is deep, and slightly gaping. 



Length -0017"; breadth 0020". 



Plate XIII. fig. 4. Front view of fronds dividing. Fig. 5. Basal view. 



H. incisa, var. ft. This variety differs only in having the extre- 

 mities of the basal lobes truncate, but not emarginate. The 

 outer angle is rounded off, whilst the inner only is furnished 

 with a mucro. 



In both forms, the mucronate spines vary in length in the 

 two lobes, and, in different specimens, from mere conical pro- 

 jections to spines equalling the diameter of the lobes in length. 

 Dimensions as in the former case. 

 Lower Bengal, 1855. 



Plate XIII. fig. 6. Front view of frond dividing. Fig. 7. Side view. 

 Fig. 8. Basal view. 



9. Micrasterias j Ag. 



Frond lenticular or tabular, deeply divided into two lobate 

 segments. Lobes dentate, or inciso-dentate. 



* Basal lobes entire. 

 1. M. expansa, Bailey. 



M. arcuata, Bailey (Smithson. Cont., Microsc. Researches in 

 S. Carolina and Georgia). 



The entire character of the basal lobe in this species denotes 

 the link between the last and the present genus. 



Var. 7, in like manner with M. arcuata, Bailey, is only a 



