$52 5%. Nostoc. 2. THALASSIOPHYT AL. Pl. cell. aph. 
4 Nostoc pruniforme. Plumshape nostoch. 
Thallus blackish, globose, solitary, solid, leatherlike, 
gelatinous, smooth. 
Ulva praniformis, Lin. S. P. 1633. 
Tremeila pruniformis, Roth Germ. 548. 
Linckia prunifurmis, Roth Cat. 3, 343. 
Nostoc pruniforme, dgardh Syn. 134. 
Adhering to trees, or floating in lakes; summer. 
Thallus gelatinous on the inside, coriaceous on the out- 
side. 5 
5. Nostos sphericum. Spherical nostoch. 
Thallus black green, globose, solid, smooth, aggregated. 
Ulva pruniformis, Hudson Fl. Angl, 572, not of Eng. Bot. 
Conferva Pyrum, Fl. Dan. 660, not of Linnzus. 
Nostoc sphericum, Vaucher, 223. 
Linkia granulata, Roth Cat. 3, 342. 
Lakes and stegnant waters. 
Thallus hardish, gelatinous, mostly aggregated, the size 
of peas. 
6. Nostoc ceruleum. Blue nostoch. 
Thallus small, globose, solid, solitary, smooth, pale blue, 
shining, pellucid. 
Nosioc ceruleum, 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 Musc. 21. 
Byssus Flos aque, Lin, S. P. 1637. 
Nostoc Flos aque, 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. AtcyonipEx. Thallus continuous, gelatinous, olive 
green becoming black, cellular; cells membranaceous, 
long, hexaedral; sporidia elliptical,scattered in the cells. 
XXVIII. 52. ALCYONIDIUM. Lamour. Halcyonide. 
Thallus roundish, long, gelatinous, branched, olive-green; 
inner cells large, hexaedral, outer cells slender, closed. 
— Marine. 
