Riccia membranacea Gottsche & Lindenb.

Riccia membranacea Gottsche & I/indenb.;
G. L. N. Syn. Hep. 608. 1846.
Riccia tenuis Aust. Proc. Acad. Phila. 1869: 233. 1870. Ricciella membranacea Evans, Rhodora 12: 196. 1910.
Thalli thin and membranous, rather small, 3-7 mm. long, usually once or twice dichotomous, irregularly gregarious, commonly dark-green, ccncolorous below, the dorsal surface smooth or more or less wrinkled on drying; main segments 2-4 mm. broad, rather obscurely costate; terminal segments obovate, obcordate, or suborbicular, retuse or emarginate-bifid ; margins commonly unistratose in younger parts for a width of 1^5 cells; median sulcus scarcely manifest except at apex; scales wanting or rudimentary; transverse sections sublinear or narrowly attenuate-elliptic, 8-12 times as broad as the maximum height, the dorsal outline nearly rectilinear, the ventral slightly curved; dorsal epidermis unistratose, persistent, the cells mostly 40-65 ^ in maximum diameter in surface view or more elongate and sometimes. 100-140 M. close-fitting, with occasional large and irregular, often subelliptic openings above air-chambers, the chambers large, irregularly elongate-polyhedral, separated by unistratose lamellae and showing one or two series on a transverse section, the basal tissue mostly of only 1-3 layers of cells. Monoicous; antheridial ostioles elevated 50-160 ju; capsules moderately numerous, 0.35-0.48 mm. in diameter, protuberant on the lower surface; spores brown,. 40-65 iM in maximum diameter, ovoid, ellipsoid, or subglobose, sometimes obscurely angled, destitute of a wing-margin, thickly covered with obtuse, truncate, or subacute spines 2-3 /t long.
Type locawty: Mexico.
Distribution: Connecticut to Ohio and Louisiana; Veracruz; Cuba; Porto Rico.