In describing Riella Paulsenii, the first species of the genus known to occur outside of the Mediterranean region, Porsild expresses the surmise that the distribution of the genus may prove to be still more widely extended, which is well verified by the known existence at the present time of three specimens of Riella collected within the boundaries of the United States. One of these, strangely enough, was collected by Schott as long ago as 1855, but has remained unstudied and unnoted in literature. In April, 1902, western Texas, the region from which Schott's specimens came, was visited by Professors F. S. Earle and S. M. Tracy, who secured further specimens which we consider the type of the well-marked species described below:
Riella Americana sp. nov.
Erect or ascending, 10–30 mm. high, simple or more commonly 1–4 times furcate: axis elliptical in section, 0.2–0.8 mm. wide, mostly 6–10 cells thick, root-hairs borne only on the basal parts and usually few: wing 2–5 mm. broad, rounded-falciform at apex, slightly undulate-crisped, subentire or erose, tapering toward the base and commonly deficient below the first dichotomy; cells near the axis about 60 μ in greatest diameter, those near the margin about 40 μ: scales few, small, 0.2–0.6 mm. long, linguiform and obtuse or irregularly lanceolate and subacute, those near the growing apex usually intermingled with multicellular gemmae: gemmae trichomic in origin, soon oblong or orbicular-oblong in outline, showing later a median constriction and becoming finally panduriform and subspatulate: dioicous: antheridia about 0.36 × 0.16 mm., sometimes as many as 75 (including empty loculi) in a single elongated marginal series: ♀ gametophyte, or each of its branches, maturing for the most part 3–12 sporogonia in acropetal order: involucres smooth, ellipsoidal-ovoid or at full maturity subglobose-ovoid, 1.4–1.8 mm. × 0.8–1.2 mm., narrowed rather gradually to the truncate or slightly pointed subpapillose orifice: capsule globose, 0.8–1 mm. in diameter, seta about 0.2 mm. long, mostly a trifle shorter than the ovoid-conic foot: spores dark-brown, 100–130 μ in maximum diameter (spines included); outer face bearing numerous sometimes curved spines 10–24 μ long, with dilated apices, these spines more or less connected by radiating basal membranes forming irregular reticulations; inner faces bearing conical, non-capitate spines, 3–6 μ long, with basal membranes obsolescent or entirely wanting. (Pl. 11; pl. 12, f. 21, 22).
Limpia Cañon, Texas, F. S. Earle and S. M. Tracy, April 25, 1902, no. 251; this, the type specimen, is deposited in the her-
