352 51. Nostoc. 2.THALASSIOPHYTJE. PL cell aph. 
4. Nostoc pruniforme. Plumshape nostoch . 
Thallus blackish, globose, splitary, solid, leatherlike, 
gelatinous, smooth. 
Ulva pruniformis, Lin. S. P. 1633. 
Tremella pruniformis, Roth Germ. 548. 
Linckia pruniformis, Roth Cat. 3, 343. 
Nostoc pruniforme, Agardli Syn. 134. 
Adhering to trees, or floating in lakes; summer. 
Thallus gelatinous on the inside, coriaceous on the out- 
side. 
5. Nostoc sphcericum. Sphcerical nostoch . 
Thallus black green, globose, solid, smooth, aggregated. 
Ulva pruniformis, Hudson Fl.Angl. 572, not of Eng. Bot. 
Conferva Pyrum, FI. Dan. 660, not of Linnaeus. 
Nostoc sphaericum, Vaucher , 223. 
Linkia granulata, Roth Cat. 3^342. 
Lakes and stagnant waters. 
Thallus hardish, gelatinous, mostly aggregated, the size 
of peas. 
6. Nostoc cceruleum. Blue nostoch . 
Thallus small, globose, solid, solitary, smooth, pale blue, 
shining, pellucid. 
Nostoc caeruleum, Lyngbye Hydr. Dan. 201. 
Ditches and pools on hypni; summer. 
Thallus hard, slippery, about a quarter of an inch in 
diameter. 
7. Nostoc papyraceum. Paper nostoch . 
Thallus frothy, gelatinous, slippery, easily parted, 
bluish. 
Byssus latissima papyri instar super aquam sparsa, Dillen in Raii Syn. 
57,12; Dillen Muse. 21. 
Byssus Flos aquae, Lin. S. P. 1637. 
Nostoc Flos aquae, Lyngbye Hydr. Dan. 201. 
Stagnant waters, floating; spring and summer. 
Thallus pale bluish green; when it covers ponds, they 
are said to be in flower. 
G. Alcyonideje. Thallus continuous, gelatinous, olive 
green becoming black, cellular; cells membranaceous, 
long, hexaedral ; sporidia elliptical, scattered in the cells. 
XXVII. 52. ALCY ONIDIUM. Lamour. Haley onide. 
Thallus roundish, long, gelatinous, branched, olive-green; 
inner cells large, hexaedral, outer cells slender, closed. 
— Marine. 
