Marine Alycn of Berwick-on- Tweed. 309 



9. Filaments with a thin gelatinous sheath. ... ... 10 



Filaments without a sheath, spores next to the heterocysts. 



Sphcerozyga. 

 1C. Filaments erect, forming bluish-gray patches on shells. Microchoste. 

 Filaments decumbent, forming dark-green slimy layers on mud. 



Nodularia. 



11. Filaments with a gelatinous sheath. ... ... ... 13 



Filaments without a gelatinous sheath. ... ... ... 12 



12. Filaments spirally twisted. ... ... ... Spirulina. 



Filaments not spirally twisted. ... ... ... Oscillaria. 



13. Filaments branched. ... ... ... Goniotrichum (in part.) 



Filaments simple. ... ... ... ... ... 14 



14. Filaments free. ... ... ... ... Lyngbya. 



Filaments adherent in meshes ... ... ... Symploca. 



Filaments united in bundles and surrounded by a general gelatinous 

 sheath. ... ... ... ... ... Microcoleus. 



15. Filaments free. ,.. ... ... ... Calothrix. 



Filaments imbedded in a dense mass of jelly. ... ... 16 



16. Filaments nearly parallel, fronds forming a thin expansion. Isactis. 



Filaments diverging from the base of the hemispherical or somewhat 

 flattened fronds. ... ... ... ... Rivularia. 



17. Fronds unicellular. ... ... ... ... ... 18 



Fronds multicellular. ... ... ... ... ... 19 



18. Cells small, ovoidal, prolonged into a long, root-like process at the 



base. .. ... ... ... ... Oodiolum. 



Cells large, filamentous, pinnately branching. ... Bnjopsis. 



Cells very long,cylindrical,with irregular or sub-dichotomous branches, 

 spores large, solitary, in special lateral or terminal cells. Vaucheria. 



19. Fronds tubular. ... ... ... ... Enteromorpha. 



Fronds membranaceous. ... ... ... ... 20 



Fronds filamentous. ... ... .,. .. ... 22 



20. Fronds minute, seldom more than a quarter of an inch high, distinctly 



stalked, cells quadrate. ... ... ... ... Pmsiola. 



Fronds more than quarter of an inch high, not distinctly stalked. 21 



21. Fronds composed of a single layer of cells. .. Monostroma. 

 Fronds composed of two layers of cells. ... ... Ulva. 



22. Fronds simple. ... ... ... ... ... 23 



Fronds branching. ... ... ... ... ... 24 



23. Small algse, filaments soft and flaccid. ... ... Ulothrix. 



Bather coarse algas, filaments more or less rigid, often twisted 



together. ... ... ... ... ... Chcetomorpha. 



24.* Branches small and root-like. ... ... ... 'Rhizoclonium. 



Branches distinct. ... ... ... ... Cladophora. 



* The genera Gomontia and Epicladia, which have been added to our 



Berwick list since this key was compiled, should be inserted here. The 



first named belongs to the class of perforating algae, and grows in the 



chalky shells of molluscs, forming green stains on them. The fronds are 



1 V 



