Dr. G. C. Wallich on Desmidiacea from Lower Bengal. 189 



angles/ or not precisely at their central portions; whereas in 

 such forms as are united side by side, without the interposition 

 of these bodies, by their centres, these spaces do not, and indeed 

 cannot occur. Amongst the filamentous Diatomace.ie, as for 

 instance in Triceratiwn, Biddulphia, Hydrosera, and others, 

 similar spaces are to be found, — the cornua in these organisms 

 (which are the analogues of the projecting angles of the Desmi- 

 diacese under notice) being only more largely developed. 



In Bengal occurs a variety of D. Swartzii in which the angles 

 are not " bidentate,^' but rounded and plane. This may possibly 

 be identical with the variety noticed as " D. Brebissonii, var. a" 

 in Kiitzing's ' Species Alg.' p. 190. The characters there given 

 are '^ articulorum dentibus truncatis; interaneis sex-radiatis, 

 radiis geminatim conuiventibus apice non incrassatis.''^ 



This form is quite as abundant as that with the bidentate 

 angles ; but, from the manner in which the lobes present every 

 gradation between those that are quite plain and rounded and 

 such as have the most strongly marked dentations, it seems highly 

 probable that the one variety is but a young state of the other, all 

 the other characters remaining identical. The generic character 

 derived from these processes has accordingly been omitted. 



1. 2). Swartzii. Filament triangular; joints bidentate at the 

 angles, deeply incised. End view triangular. Uniting cushions 

 cuneiform. 



In the front view the joints are quadrangular, and somewhat 

 broader than long. A deep constriction divides the joint into 

 two segments, which have an angular tooth at their margins. In 

 the end view the connecting cushions are cuneiform, their apices 

 being directed towards the centre of the joint. The space left 

 between the joints varies greatly at different periods of growth, 

 and in different specimens. In the front view of the filament, 

 the connecting cushions present minute angular projections at 

 the points of union with each other; and lastly, in the end view 

 the joints are finely granular. 



With reference to the sporangial condition of this species, 

 Mr.Ralfs remarks : " I have gathered at Dolgelly some fragments 

 of this plant which had the endochrome condensed into a spo- 

 rangium-looking body in the centre of each joint. As in every 

 other species of this family in which the reproductive body has 

 been detected it is the result of the coupling of the cells, I 

 think it best merely to direct attention to the fact I have men- 

 tioned, leaving its nature to be determined by future observa- 

 tion.^^ (Ralfs, 'British Desmidiese,' p. 62, tab. 4.) 



In the same work (Appendix: "List of Species not hitherto 

 detected in Britain/' p. 208, tab. 35. fig. 1) the following passage 



