508 Annals of the Smith African Museum. 



preted as a Selenastrum by Lagerheim and others. In all the 

 specimens examined, however, the irregular groups of cells did not 

 partake of the character of a Selenastrum, in which it is characteristic 

 for the cells to be arranged back to hack; rather, in these irregular 

 forms of S. acuminatus, the cells arc arranged anyhow (which of 

 course may include an occasional Selenastrum -like grouping) and bear 

 more resemblance to an Ankistrodesmus (Raphidium) than to a Sele- 

 nastrum. Moreover, in Selenastrum the chloroplast appears to fill the 

 cell completely. 



The form figured by West in his British Freshwater Algae 

 (p. "225, Fig. 95, E-G), under the name of Selenastrum acuminatum, 

 Lagerh., does not appear to me to be the same as the form originally 

 described and figured by Lagerheim under that name. The grouping 

 is that typical of a Selenastrum, the cells are often much more strongly 

 curved, and they do not have hyaline tips, the cell-contents extending 

 to the very apex. This form I have also seen at the British Museum 

 (on a slide labelled "No. 852, Bowness, Lake District, W. & G. S. 

 West"). For West's form I suggest the name of Selenastrum westii, 

 nov. nom. 



Brunnthaler (op. cit.,-p. 170) regards Scenedesmus dimorphus, Kuet- 

 zing (= S. obliquus (Turp.), Kuetz., var. dimorphus, Eabenh.) as 

 synonymous with S. acuminata* (Lagerh.), Chod. There can be no 

 doubt that some of the forms described as S. obliquus, var. dimorphus, 

 are referable to S. acuminatus (e. g. the form in Fig. 10, p. 274, in E. 

 Teiling, Schwed. Planktonalg., I, Bot, Tidsskrift, vi, 1912), but it 

 seems open to question whether the true var. dimorphus of S. obliquus 

 is not really distinct from S. acuminatus. There are the following 

 important differences between these two forms. In S. obliquus, var. 

 dimorphus, the tips appear more definitely as outgrowths of the cells 

 (cf. Fig. 7, c and d), the latter narrowing down rather suddenly to 

 produce them. Further, the central cells are fusiform, with both inner 

 and outer surfaces curved (Fig. 7, c, d), whereas in S. acuminatus the 

 outer surfaces are always flat : the outer cells in the var. dimorphus 

 have the outer faces flat for a considerable distance and are not 

 uniformly curved as in S. acuminatus. Finally, the outgrowths are in 

 general far shorter (Fig. 7, c), and only rarely attain to a length 

 approaching that found in »S'. acuminatus (Fig. 7, d). 



3. Scenedesmus guadricauda (Turp.), Brcbisson, Alg. Falaise, 

 1835, p. 66; Brunnthaler. op.cit., p. 168, Fig. 10. 

 Forma typica. 



Samples' 14, 15, 18, 39.48. 



