128 NEMATOPHYCEE. 
Famity I. ULVACEA. 
Thallus membranaceous, or foliaceous, rarely crustaceous, 
formed of one stratum of cells, either expanded, or tubulose, or 
vesiculose. 
Propagation by zoogonidia, arising from a repeated division 
of the cytioplasm. Zoogonidia oblong, furnished at one ex- 
tremity with two or four cilia. 
Sub-Family 1. PRasioLes. 
Thallus expanded and foliaceous, rarely crustaceous. 
Genus 54. PRASIOLA. 4g. (1821.) 
Thallus membranaceous foliaceous, ascending or erect, more 
or less crispate, composed of angular cells, distributed in plane 
areas ; base sometimes loosely fibrillose. 
Vegetation by division of the cells in two directions. 
Prasiola crispa. Kutz. Tab. Phyc. V. t. 40, f. 6. 
Tufts more or less dense, often long and widely expanded, 
dark green, soft and elastic. Thallus plicate crisped, of variable 
form and size, often bullate; cells arranged in distinct areolas, 
or confluent, quadrate, or oblong-quadrangular, now and then 
twice as long as the diameter; angles more or less obtusely 
rounded. 
Size. Cells -005-:009 mm, diam., or °008-:013 mm. x 
003-005 mm. 
Jessen Mon. Pras. t.1, f. 10-16. Rabh. Alg. Eur. iii, 308. 
Lagerstedt, Pras. p. 19. 
Ulva crispa, Hass. Alg. t. 78, f. 12. Eng. Flora v., p. 312. 
Eng. Bot. ed. i, 2754; ed. ii, 2406. Lightf. Fl. Scot. 972. 
Harv. Man. 171. Grev. Fl. Edin. 299. Hook Fl. Scot. ii., 91. 
Mack. Fl. Hib. 243. Hull Br. Fl. 309. Abbot. Fl. Bedf. 273. 
Johnst. Fl. Berw. ii., 250. Jenner. Tunb. Wells 190. 
Ulva lactuca y, Huds. Fl. Ang. p. 567. Dillen. Muse. t. 9, 
f. 6. 
Ulva terrestris, Gray. Arr. i., 344. 
Tremella crispa, With. Ary, iv., 81. 
On damp ground, rocks, &e. 
Hassall unites this species and the next together in one, but his 
example has not been followed by his successors. 
Common on moist. shady ground, especially near houses and walls, 
sometimes on old thatched roofs. Fronds very much crowded, forming 
a dense stratum, rather lying on the soil or medium than attached to it; 
deep green, rounded, thin, tender, but not gelatinous, variously corled 
