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



the new generic name of Tetrachastrum in the f Nat. Hist. Re- 

 view ' (vol. vi. No. 4. p. 464) ; but, if a mature form, the entire 

 absence of any inflated protuberance, or terminal notch, would 

 seem sufficient to distinguish the latter from the present species, 

 and to render it conformable, in all essential characters, to 

 Holocystis oscitans, Hassall. 



In the side view, the central inflated portion presents an 

 irregular granulated outline, and the segments are pyriform. 

 End view broadly elliptical, with the inflated portion granulated 

 and the angles furnished with several stout conical projections. 



The lateral margins, in the front view, are sinuate, the pro- 

 minent portions presenting the conical projections already 

 referred to. 



Length -0050"; breadth '0038'. 



Lower Bengal, 1855. 



Plate XIV. fig. 17. Front view. Fig. 18. Side view. 



8. E. clepsydra, n. s. Frond quadrangular. Segments broadest 

 at the terminal margin, and acutely constricted on their 

 lateral margins. Angles rounded. 



Frond rather longer than broad, much inflated. Terminal 

 margin straight, and crenate between the rounded angles. 

 Surface granulated. 



Side view oblong, truncate, the extremity angular and sub- 

 dendate. The central constriction marked by a sinuosity. End 

 view elliptical. 



Length -0013" ; breadth at outer margin -0014". Ditto at 

 constriction -0009". 



Lower Bengal, 1855. 



Plate XIV. fig. 19. Front view. Fig. 20. Side view. Fig. 21. End 

 view. 



**** Lateral lobes distinct, entire. 



9. E. commissurale, Breb. Frond divided by a somewhat gaping 

 but deep constriction into two segments. Lateral lobes hori- 

 zontal, entire. Terminal lobe direct, slightly emarginate, or 

 notched. Lobes with central and terminal granular protu- 

 berances. 



Cosmarium commissurale, Breb. 



Although not in possession of authenticated specimens of 

 Cosmarium commissurale, Breb., from very careful comparison 

 of the truncated Bengal variety with the description and figures 

 of that species given by Mr. Ralfs (British Desmid.), there can, 

 I believe, be little doubt of their identity. The occurrence of the 

 other variety with a large, somewhat inflated, angular terminal 

 lobe, as also the presence, on that and the basal lobes, of the 



