EVANS—THE NORTH AMERICAN SPECIES OF ASTERELLA. 261 
h. Pseudoperianth with purple segments___--~-- 7. A lindenbergiana (p. 283). 
h. Pseudoperianth white or pale throughout__-_ -- - -- 4, 
i. Thallus 1.5 to 4 mm, broad, the margins not closely undulate-crispate. 
8. A. venosa (p. 286). 
i. Thallus 8 to 10 mm. broad, the margins closely undulate-crispate, 
9. A. rugosa (p. 289). 
j. Not xerophytic, the margins scarcely or not at all incurved when dry_--. k. 
j. More or less xerophytic, the margins incurved when dry; sexual branches 
short; spores with coarse reticula on the faces, the meshes mostly 15 to 
20 w in diameter_-__ -o---- eee +++ --- n. 
k. Male branches variable in length; spores with coarse reticula on the faces, 
the meshes 8 to 20 » in diameter____-_- _- -- _- 1, 
k. Male branches short; spores with fine and irregular reticula on the faces, 
the meshes mostly 2 to 8 w in diameter___-__ 15. A. versicolor (p. 307). 
1. Meshes on spore surface mostly 15 to 20 w in diameter__--------_-------- m, 
1, Meshes on spore surface mostly 8 to 12 » in diameter. 
13. A. reticulata (p. 302). 
m. Tubercles of female receptacle less than 0.5 mm. long. 
10. A. elegans (p. 290). 
m. Tubercles of female receptacle 0.5 to 1 mm, long, 
11. A. echinella (p. 298). 
n. Psudoperianth mostly 8 to 10-cleft; reticula on spore surfaces rarely in- 
volving the marginal wings; elaters mostly 12 to 14 w wide. 
12. A. lateralis (p. 299). 
n. Pseudoperianth mostly 10 to 16-cleft; reticula on spore surfaces usually in- 
volving the marginal wings; elaters mostly 8 to 12 » wide. 
14. A. bolanderi (p. 303). 
1. Asterella tenella (l.) Beauv. 
Marchantia tenella L. Sp. Pl. 1187, 1758. 
Asterella tenella Beauv.; Lam. Dict. Sci. Nat. 3: 257. 1805 (7). 
Fimbriaria tenella Nees, Hor. Phys. Berol, 45. 1820. 
Fimbriaria nigripes Bisch.; Lehm. Nov. Stirp. Pugill. 6: 19. 1834, 
Fimbriaria tenella B porphyrocephal. Bisch. Nov, Act. Acad. Caes. Leop. 
Carol. 17: 1023. pl. 69, f. IY. 18385. 
Fimbriaria tenella y brachypus Gottsch., Lind. & Nees, Syn. Hep. 563. 1847. 
Fimbriaria brachypus Mont. loe. cit., as synonym. 
Fimbriaria mollis Tayl. Lond. Journ. Bot, 5: 411. 1846. 
Hypenantron tenellum Trevis. Mem. Ist. Lombardo III. 4: 440. 1877. 
Hypenantron molle Trevis. op. cit. 441. 1877. 
Thallus bright green, often more or less pigmented with purple, especially on 
the ventral surface and along the margin, mostly 0.5 to 1.5 cm. long and 1.5 to 
3 mm. wide, plane or somewhat concave, with undulate margins, branching 
regularly by forking, very rarely by ventral outgrowths, keel broad and rounded ; 
epidermis composed of cells with slightly thickened walls, sometimes showing 
trigones, averaging about 40 X 25.4; pores slightly or not at all elevated, aver- 
aging (with their surrounding cells) about 40 X 80 w; surrounded by (4 to) 6 
series of cells with 2 (or 3) cells in each series; cells containing oil bodies few 
and scattered, occurring in the epidermis, the green tissue, and the compact 
ventral tissue; green tissue loose, the air chambers in 4 or 5 layers (in the 
median portion), those of the dorsal layer larger than the others, not subdi- 
vided, each with an epidermal pore; compact tissue occupying about half the 
thickness of the thallus in the median portion, thinning out gradually on the 
sides and extending about halfway to the margin, composed of cells with more 
