NEW TO BRITAIN IN 1880. 207 



to Britain, is Staurastrum arctiscon, Ehr. It was first described by 

 Ehrenberg. Then it seems to have been lost sight of for years, 

 until it was found in Sweden, next in Ireland, and now in Wales. 

 It is probable that Bailey found the same species in the United 

 States. 



This species forms one of a group of closely allied species, of 

 which Staurastrum fur ciger urn, figured by Ralfs, is one, the present 

 species another; Staurastrum pseudofurcigerum, Reinsch, is a third. 

 Staurastrum sexangulare, Bulnh., is a fourth, and a species figured 

 by Wood in his Fresh-Water Alga3, if really distinct from Stau- 

 rastrum arctiscon would be a fifth. Of these, all except the last, 

 have now been found in the British Isles. Mr. Wills found two at 

 Capel Curig, Staurastrum pseudofurcigsrum and Staurastrum 

 arctiscon, the former for the first time, the latter had been found in 

 Ireland, as also has St. angulare. The diagrams will convey a 

 better idea of the complex forms of these species than verbal de- 

 scriptions, special attention being directed to the end views. 



Dismissing these we come to a singular form, in which the arms 

 are all in the same plane, towards the apex of each semi-cell. This 

 is Staurastrum opTiiura, Lund. It is another large species, figured by 

 Lundell with seven arms, but all the Welsh specimens have 

 invariably eight arms, and the proportions of the cells seem slightly 

 different, being longer than in Lundell's figure. Previous to its 

 discovery in Britain, Staurastrum arachne, Ralfs, was the nearest 

 species, but that is very much smaller, beside other differences. 



Staurastrum cerastes, Lund., is a characteristic but smaller 

 species. Each semi-cell is crowned by three or four stout ornate horns, 

 which are bent towards the centre, until the tips of the horns of the 

 two semi-cells nearly meet. This Swedish species had been found 

 in Ireland previously, and now at Capel Curig. It was included in 

 a gathering made also by Mr. Wills at Barmouth many years ago, 

 but only recently determined. 



Staurastrum Sehaldi, Reinsch., resembles Staurastrum vestiturUy 

 Ralfs, but is larger and more elaborately ornamented. Mr. Archer 

 found it in Ireland, and Mr. Wills a variety of it at Capel Curig. 

 I have compared the specimens from Wales with those on a slide 

 mounted and named by Reinsch himself. The ordinary form is tri- 

 radiate, but in the front view only two arms are usually seen at once 

 at each semi- cell, one on each side. The Welsh form has longer 

 arms, but the differences appear to be only varietal. 



JouRN. Q. M. C, No. 46. r 



