806 Transactions. — Botany. 



dence in favour of distinctness of species. And, in fact, taking a gradation 

 from M. ampullacea, through M. foliacea, M. americana, and the rest, to M. 

 rotata, why should they not all be simply varieties ? When, indeed, it has 

 come to be thoroughly understood what a "variety " is, and what a " species " 

 is, all doubts can be cleared up. Meanwhile, I offer my M. ampullacea as a 

 distinct, and, I venture to think, an elegant species of the genus. 

 5. Holocystis, Hassall. 



Micrasterias, Ealfs. 

 This genus is separated from Micrasterias by having the lateral lobes 

 almost or quite parallel, not radiant. But the distinction seems scarcely 

 sufficient. Ealfs, who wrote after Hassall, refuses to accept his nomencla- 

 ture, pointing out that the dentation at the extremity of the lobes is scarcely 

 consistent with the proposed name. However, as Mr. Hassall's name has 

 been accepted by later writers, I leave it here. 

 H. incisa. 

 Micrasterias incisa, Kiitzing. 



Figure 24. 

 I believe this plant to be identical with one from Bengal, described and 

 figured by Dr. Wallich.* It is there called a " variety " of Kiitzing's 

 species, but I have not seen the original plant. Dr. Wallich makes two 

 varieties, in one of which the edge of the terminal lobe is emarginate ; in the 

 other it is not so. The plant here, as shown in my figure, exhibits both 

 characters ; this is due to the immaturity of the non-emarginate segment. 

 When fully grown, both segments are emarginate. 

 6. Euastrum, Ehrenberg. 

 E. elegans, Brebisson ; or, E. binale, Turpin. (R. XIV.) 

 Rare. 



Figure 26. 

 I have seen two specimens (one of which I have preserved). The plant 

 maybe of either of these species, though it maybe probably 7?. binale, as the 

 sides of the terminal notch do not extend beyond the lateral spines. Both 

 species are extremely minute, from g^ to x"45^ of an inch long, and some- 

 what variable. 



7. Cosmarium, Corda. 

 C. ralfsii, Brebisson. (R. XV.) 

 Common. 



C. meneghinii, Brebisson. (E. XV.) 

 Not uncommon. 

 C. crenatum, Ealfs. (R. XV.) 

 Rare. 



* " Ann. and Mag. of Nat. Hist.," Vol. V., third series, 1860. 



