STAURASTEUM. 143 



Rkiconich, Sutherland ! Common in the plankton of 

 Lochs nan Cuinne, Ghriama and Ruar, Sutherland ; 

 Loch Luichart, Ross, and Loch Bairness, Inverness ! 

 In the plankton of 10 lochs in Lewis and Harris, Outer 

 Hebrides, and in the plankton of the Shetlands. 



IRELAND. - -Donegal ! Gal way ! Kerry! London- 

 derry ! In plankton, Galway, Kerry, Lough Neagh, and 

 Lough Beg, Londonderry ! 



Geogr. Distribution.- -Norway. Sweden. Finland, 

 Denmark. United States. 



There are apparently two distinct forms of this Desmid, 

 although the fact was never commented upon by Professor 

 West. The ordinary form, figured by Cooke, is the larger 

 of the two (cf. PL CXLVI, fig. 7). It has a broadly fusiform 

 ' body," and short, stout diverging processes, tipped with 

 2 or 3 large spines. The other form (see PL CXLVII, fig. 1), 

 is exactly similar in shape, or sometimes the * body ' of the 

 semicell is more cup-shaped, but it is much smaller, and some- 

 times the processes are relatively longer. The granulation of 

 the cell differs from that of the larger form, in that there is only 

 one row of verrucse across the top of the semicell ; in the vertical 

 view the marginal series of verruca is wanting, onlv the row 



c? o ' / 



within the margin being present. This form was recorded by 

 Professor West from the plankton of Loch Cuthaig (W. & G. S. 

 West, 'Further Contrib. Plankton Scottish Lochs,' 1905, p. 487), 

 without any reference being made to its differing slightly from 

 the form figured by Cooke & Wills. Professor West's drawing 

 of this Desmid from the above Scottish locality is reproduced on 

 PL CXLVII, fig. 1. The writer has also observed this smaller 

 form in material from the lower lake at Capel Curig. These 

 specimens occurred in great abundance along with the larger 

 and typical form. The small forms from Capel Curig are more 

 like the large typical form than the small specimens from 

 Loch Cuthaig, but in both cases the cells are constantly 

 smaller, and the marginal series of verrucae is wanting in the 

 vertical view. Furthermore there is always a difference in the 

 chloroplasts of the two forms. The larger one has an axile 

 chloroplast with a pyrenoid in each angle of the semicell, i. e. 

 typically 3 pyrenoids in the ordinary triangular specimen (see 

 Carter, 'Chloroplasts of Desmids,' IV, 1920, t, xiv, f. 19, 20). 

 The smaller form, however, has only a central pyrenoid in each 



