196 Rhodora [OCTOBER 
suggests that the name R. minima be given up altogether and that 
both R. nigrella and R. sorocarpa be known by the names under which 
they were first clearly distinguished. 
2. Ricciella membranacea (Gottsche & Lindenb.) comb. nov. 
Riccia membranacea Gottsche & Lindenb.; G. L. & N. Syn. Hep. 608. 
1846. Riccia tenuis Aust. Proc. Acad. Philadelphia for 1869: 233. 
In a dried up ditch. Hartford, Connecticut (E. B. Harger and Miss 
Lorenz). New to New England. The type locality of R. mem- 
branacea is in Mexico, while that of Riccia tenuis is in New Jersey. 
The latter species was considered distinct until Stephani! reduced it 
to synonymy in his Species Hepaticarum. According to Underwood ? 
it occurs in New Jersey, Delaware, Ohio, Missouri, and Arkansas. 
The writer has found it also near Cayey, Porto Rico, and the speci- 
mens from this locality agree closely with those from Hartford. If 
Spruce's Riccia lanigera, as Stephani asserts, is likewise to be con- 
sidered a synonym of R. membranacea, then the range of the species 
extends well into South America. Spruce's description, unfortu- 
nately, disagrees in several important respects, so that the identity of 
the two species cannot yet be regarded as thoroughly established. 
The plants of R. membranacea bear considerable resemblance to the 
prothallia of ferns. They grow closely appressed to the ground, 
sometimes scattered, sometimes more or less crowded and forming 
irregular mats or patches. They are dark green but often appear 
somewhat paler on account of the air in the large intercellular spaces 
described below. The thallus is broad and thin, practically plane 
on the upper surface, and usually forks only once or twice. It meas- 
ures from 3 to 5 mm. in length, and the broad divisions, which are 
truncate and narrowly indented at the apex, are 2 to 3 mm. wide. 
The texture of the thallus is exceedingly delicate, and the central 
region, except where the sporophytes are situated, is rarely more than 
0.3 mm. thick. From this central region the wings gradually thin 
out toward the edge, which is bordered by a margin about three cells 
wide and only one cell thick. Even in the median part of the thallus 
the solid basal tissue is only a few cells thick and quickly becomes 
reduced to a single layer in the wings. The bulk of the thallus is 
made up of a loose photosynthetic tissue in which the air spaces are 
! Bull. de l'Herb. Boissier 6: 361. 1898. 
? Bot. Gaz. 19: 278. 1894. 
3 Hep. Amaz. et And. 570. 1885 
