28 Illinois State Lahoratori/ of Xatiiral History. 



JM. R. tenuis Aust. Thallus thin, olive or yellowish 

 green, shining; divisions 2 or 4, expanded, roundish-obovate, 

 plane, 4—8 mm. long, the margins sinuate; beneath green, 

 narrowly carinate by a slender costa, with a few delicate root- 

 lets; fruit in the nerve; capsule extremely delicate, closely ad- 

 hering to the substance of the thallus, crowned with a minute 

 oblong style; spores round or short oval with a conspicuous de- 

 pression in one end when dry, bursting through neither surface 

 of the thallus. 



Hab. — Wet broken ground in open woods. Closter, N. J. (Ausfin), 

 near Lawrence, N. J. (James), Mo. {Hall). 

 Bib.— Pro. Phil. Acad. 1869, p. 233. 

 Exsic. — Hep. Bor.-Amer. No. 150. 

 ** Thalli dimorphous or polymorphous, pseudo-aquatic. 



19. R. fluitans L. Thallus thin, green, orbicular, radi- 

 ately expanding, 2.5 — 5 cm. in diameter, floating, often form- 

 ing extensive patches ; divisions often much imbricated or some- 

 what entangled, narrowly linear, usually 1 — 1.5 mm. wide, re- 

 peatedly forking, fibrous-nerved in parallel lines, plane above, 

 convex and eradiculose beneath, cavernous only toward the 

 apex; apices slightly dilated, very obtuse or subtruncate, emar- 

 ginate; fruit present only in some terrestial forms, very prom- 

 inent below, at length rupturing beneath the thallus. (Bicci- 



ella fu items Al. Braun.) Forma lata has a broader 



thallus and a minute patch of fuscous purple, triangular scales 



at the extremities of the divisions underneath; sterile. 



Forma nodosa f'^. nodosa Bouch. ) has the thallus here and 



there tuberously thickened; sterile. i^or;;?a canaliculata 



(E. caiialirulata Hoffm.) is small, pale, terrestrial from drying 

 up of waters on which it floated ; divisions narrower and thick- 

 er, more or less channeled above, radiculose beneath; rarely 



fertile. Forma terrestris is darker green with divisions 



shorter and slightly depressed-canaliculate above; usually fer- 

 tile. Passes through the above forms to 



Var. Sullivanti Aust. Thallus orbicular^ radiately much 

 divided, cellular-succulent, shining, yellowish green, 0.6 — 1.7 

 cm. in diameter; divisions twice or three times forked, linear, 

 about 1 mm. wide, straight, canaliculate above, carinate thick- 



