W. WEST AND G. S. WEST: ALGA-FLORA OF YORKSHIRE. 137 



S.W. — On submerged twigs, Frizinghall (iii. 1897). 

 N.E.— Carlton Bank. 



Class MYXOPHYCEiE. 

 Order HORMOGONE^. 



Sub-Order Heterocyste^. 



Family RIVULARIACE^. 



Genus AMPHITHRIX Kutz., 1843. 



671. Amphithrix janthina (Mont.) Born, et Flah. 

 Mid W.— On inundated stones, Cowside Beck, Arncliffe. 

 N.W. — Mossdale Moor, Widdale Fell (iv. 1897) on dripping 



limestone rocks with Dactylococcus bicaiidatiis var. subramosiini. 



This species has not previously been recorded for the British 



Isles. 



Genus CALOTHRIX Ag., 1824. 



672. Calothrix parietina (Nag., 1849), Thur., 1875. 

 Mid W.- — Simon's Fell (iv. 1892). On inundated stones, 



Cowside Beck, Arncliffe. 



N.W. — Vertical face of dripping rocks. Hell Ghyll Beck. 



673. Calothrix balearica Born, et Flah., 1886. 

 Var. tenuis West & G. S. West. 



A variety with the filaments only about half the thickness of 

 the type. The filaments are very tortuose and intricate, and 

 heterocysts are absent. Thickness trich. 3*5-5 jw. The sheaths 

 are mostly truncate, and in older filaments are of a characteristic 

 smoky-brown colour. 



Mid W.— Simon's Fell (iv. 1892). 



Genus RIVULARIA (Roth.) Ag., 1824. 



674. Rivularia haematites (DC, 1806) Ag., 1824. 



[Syn. Zonatrichia calcarea Endl, 1843 ; Z. rivularis 

 Rabenh., 1865 ; Z. fliiviatilis Rabenh., 1865]. 

 Mid W, — Forming hard lumps on stones in streams in lime- 

 stone districts. Abundant in Gordale. On rocks over which the 

 water was running quickly. Penyghent. Ingleton, near Thorn- 

 ton Force. 



N.E. — Moorland rill, near Scarborough. 



