PORELLA. 87 



4. Porella rivularis {Nees), Lindb. 



Madotheca rivularis, Nees, Ntit. Eur. Leb. 3, p. lt)(5 (1838). 

 Porella rivularis (Nees), Lindb. Muse. Scand. p. 3 (1S7!)). 



Dioicous, depresso-csespitose, medium to largish in size, 

 varying in colour from pale to dark olive or brownish-green, when 

 dry often yellowish-green. Stems irregularly pinnate or sub- 

 dichotomous, apices often subfastigiate, somewhat firm, frontally 

 compressed, 1 5 x 20 cells in diameter; cortical cells very small 1-3, 

 outer rows reddish-brown, inner much larger, hyaline. Leaves 

 approximate, slightly appressed, incubous, horizontal or horizontal- 

 patent-divergent, unequally bilobed, antical lobe much the larger, 

 almost plane, obliquely rotund-ovate, apex slightly decurved, 

 margin distantly denticulate or subentire, usually with 1-3 large 

 teeth at the antical base ; postical lobe or lobule erect or erecto- 

 patent, contorted, much decurrent, obliquely ovate or ovate- 

 lanceolate, acute, sometimes uncinate, margin recurved, undulate, 

 repand, subentire or denticulate, often with lew large teeth near the 

 base ; texture somewhat thin but firm, epidermis dull, rarely with 

 a slight polish, cells medium size, roundish, walls thin, trigones 

 very distinct. Stipules appressed to stem or slightly recurved, 

 very decurrent, quadrate- oval, apex rotundate, margin reflexed, 

 undulate, repand, subentire or dentate, especially at the base. 

 Flowers ? produced on short lateral branches, nearer the postical 

 than the antical side of stem ; bracts about 3 times smaller than 

 the leaves, unequally bilobed, antical lobe oval, apex acute, margin 

 entire, postical lobe aljout half the size, quadrate-oval, margin 

 quite entire ; bracteole small ovate-quadrate, retuse, margin quite 

 entire. Perianth broadly oval, complanate, mouth small, sub- 

 entire. Pistillidla about 8. Androscia on short lateral branches, 

 small ; perigonial bracts closely imbricate, 4, 5 pairs, unequally 

 bilobed, complicate-concave, antical lobe oval-oblong, margin 

 entire, postical lobe half the size, oblong-quadrate, margin (|uite 

 entire. Antheridia oval. 



Dimensions. — Stems U- to 2 inches long, -4 mm. to '5 mm. in 

 diameter, witli leaves 4- mm. wide; leaves, antical lobe 225 mm. 



