NOSTOCEA, 227 
8 Trichomes homogenous, regular. 
1. Frond very small ; trichomes very 
compact ‘ . . 22. minutissimum. 
2. Frond attaining 2. 10 mm. 
* Joints spherical, compressed . 23. gregarium. 
** Joints discoid, very compact . 24. edule. 
3. Fronds attaining the size of a nut 25, PRUNIFORME, 
VI. Vrrerucosa. Aquatic species. Fronds rounded or discoid, at first 
full, then hollow, limited at the circumference by a firm and tough 
periderm, Trichomes thin, very regular, spaced out and a little 
flexuous at the centre, more compact, and very distorted at the peri- 
phery. 
a. Fronds subglobose or warted. Mucilage 
tolerably soft. Trichomes medium com- 
pact, and often ae of sheaths at 
the periphery . . 26. VERRUCOSUM. 
b. Fronds at first discoid or tongue- shaped, 
a little ovoid, hard; trichomes radiating 
regularly from the centre to the circum- 
ference and there eee a very dense 
layer é : - «27, parmelioides. 
VII. ZETTERSTEDTIANA, Aquatic species, Fronds spherical, hard, 
tuberculose, divided into radiating separable 
lobes . ‘ : soe ee, 28, Zetterstedtit. 
VIII. -FLAGELLIFORMIA. Terrestrial species. Fronds forming thongs, 
linear straight, and very long. 
Frond linear or setaceous, subdichotomous 
trichomes longitudinally parallel. . 29. flagelliforme. 
I, Intricata. Species aquatic, fronds soft, gelatinous without 
determinate form, often floating. 
Nostoc Linckia. (Roth.) Born § Thur. Notes Alg. p. 86, t. 28, 
f. 1-12. 
Fronds lobed, multipartite, free swimming, as large as a 
walnut, lobes elongated and anastomosing, eruginous green, at 
length becoming brownish. 
Trichomes flexuous, aggregated, joints short and close, 
spherical, or spherical compressed, sheaths uncoloured, very 
refractive. Heterocysts slightly oblong. Spores subglobose or 
oval. 
Size. Joints ‘0035 mm., heterocysts :005-:006 mm. diam., 
spores (in form intricatum) subglobose (0065 x -0U9 mm. 
Rivularia Linkia, Roth. Neue Beitr. p. 263, 
Nostoc confusum, Ag. Syst. Alg. p. 22. 
Monormia intricata, Berk. Glean. t.18. Hass. Alg. 286, t. 
75,f. 11. Ralfs. Ann. Nat. Hist. 1850, p. 326, t. 8, f. 1. 
Anabaena intricata, Kutz. Phyc. Germ. 171. Rabh. Alg. 
Eur. ii., 183. 
Anabaena flos-ague, Rabh. Alg. Sachs, No. 27. 
