206 M. C. COOKE ox SOME DESMIDS 



rastrum grande of Bulnheim (^' Hedwigia," t. ix. A, f. 14), '084- 

 •088 mm. to -1 mm. long, and •08-'082 mm. or more broad, which 

 is large for a Staurastriim ; each semi-cell is elliptical, without pro- 

 cesses, and the end view triangular with obtuse angles, and slightly 

 concave sides. The endochrome is banded. It was first found in 

 Germany, then in Sweden, and now in Wales. The characteristics 

 are so distinct that it cannot well be confounded with any other 

 species. 



A smaller species is Staurastrum aversum, Lund., which is some- 

 what similar to Staurastrum hrevispina, Breb. It was found in 

 Ireland by Mr. Archer, but this is" its first aj)pearance in Britain. 



Its length is about •045--05 mm., and its breadth -036- 042 mm. 

 The semi-cells are somewhat elliptical, slightly concave on the outer 

 margin, and bearing a minute rounded nodule on each side. The 

 end view is three-sided, with rounded angles, and a rounded nodule 

 at each angle ; the sides are slightly concave. By comparison of 

 the figures with tliose of its nearest ally, Staurastrum hrevispina^ 

 on the same diagram, tlie diflerences will be manifest. 



A larger species, with somewhat similar outline, except that the 

 outer margin of the semi-cells is slightly convex, is Staurastrum 

 longispinum. It was first discovered many years ago by Bailey, in 

 the United States,^ afterwards it was found in Sweden, then it was 

 recorded in Ireland, and now in North Wales. It is certainly a 

 fine species, with two spines on the outer margin on each side of 

 each semi-cell. The end view is three-sided with rather obtuse 

 angles, armed with a long straight-pointed spine, and the sides are 

 slightly concave. The endochrome is in fillets, as in Staurastrum 

 grunde. The cells are from -1 mm. broad and long. 



Although this, and others, may be described as triangular in the 

 end view, specimens may be met with in which the end view is 

 quadrangular. This fact should be remembered, as species often 

 vary in this direction. 



A still more magnificent species is Staurastrum brasiliense, 

 Nordst., first found in Brazil, afterwards in Sweden, and now in 

 Wales. It has not been recorded in Ireland. Tlie figure on the 

 diagram will give a better illustration than a technical description. 

 In the front view it certainly has a striking resemblance to a species 

 of Xanthidiuni, but the five or six angled end view determines it to 

 be a Staurastrum. In size the frond is nearly -1 mm. long and 

 about '08 mm. broad. 



Another species which, although once recorded in Ireland, is new 



