PLEtfEOT ENIUM. - 



peripheral ring of (3-8 conical teetli (wliicli do not pro- 

 ject beyond the extreme apex) ; cell-wall smooth or 

 distinctly punctate. 



Zygospore unknown. 



Length 280-520 /u, ; maximum bread tli 40-80 /A ; 

 breadth of apices 24-50 /JL. 



WALES. ( 1 ;ipel Curig, Carnarvonshire! (Cookc tj* 

 Wills). 



SCOTLAND. Rhiconich and Lower Duartmore, 

 Sutherland! 



IRELAND. Connernara, Galway (Archer). 



< }<'(>tjr. Distribution. Germany. Galicia in Austria. 

 Norway. Sweden. India. Ceylon. Singapore. Java. 

 New Zealand. United States. Brazil. 



This is one of the most handsome of the British species of 

 Pleurotsenia, and it is also one of the rarest, being confined 

 to certain of the rocky districts of the west coast. It is a 

 somewhat variable species, especially in the relative pro- 

 minence of the rings of nodules, in the shape of the nodules 

 themselves, and in the width and degree of extension of the 

 apex. The apical teeth were not illustrated by Bailey (in 

 Knit's' Brit. Desm. t. 35, f. 8), but that was purely an oversight. 

 They are present in all specimens of PL nodosum, both 

 American, European, Asiatic, and Australasian. We were at 

 first inclined to believe that all the British examples were of 

 comparatively small size, but we have since obtained Scottish 

 specimens equal in size to the largest American or Asiatic forms. 



There is no excuse for the names " a. tyfiica" and " j. <lcn- 

 tata " given by Turner to forms of this species. If Turner 

 had examined a sufficient number of specimens from different 

 localities, he would have found that all were dentate at the 

 apex, and that the species was not exceptional in the matter 

 of variation within certain limits. 



Turner also describes "ft. anglicum'' from Capel Curi^, 

 N. Wales (Wills), and from near Windermere (Turner) ; vide 

 ' Freshw. Alg. E. India/ 1893, p. 35. He says that near the 

 apex are 10-12 small nodes or hollow tubercles, but his figure 

 gives one the impression that the apex was in an oblique 

 position when sketched. We have examined a number of 

 specimens of this Desm id from Capel Curig, collected over a 

 period of nine years, and have always found the apices 

 typical. 



