Howe and Underwood: The Genus Riella 218 



In describing Riella Paulscnii, the first species of the genus 

 known to occur outside of the Mediterranean region, Porsild ex- 

 presses 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. no v. 



Erect or ascending, 10—30 mm. high, simple or more com- 

 monly 1-4 times furcate : axis elliptical in section, o.2-o.(S 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 fi in greatest diameter, those near the 

 margin about 40/>«: scales few, small, 0.2-0.6 mm. long, lingui- 

 form 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 

 X 0.16 mm., sometimes as many as 75 (including empty loculi) 

 in a single elongated marginal series : 9 gametophyte, or each of 

 its branches, maturing for the most part 3-12 sporogonia in acro- 

 petal order : involucres smooth, ellipsoidal-ovoid or at full maturity 

 subglobose-ovoid, 1.4- 1.8 mm. x 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/^ in maximum diameter (spines included) ; outer 

 face bearing numerous sometimes curved spines 10— 24/i long, 

 with dilated apices, these spines more or less connected by radiat- 

 ing basal membranes forming irregular reticulations ; inner faces 

 bearing conical, non-capitate spines, 3-6// long, with basal mem- 

 branes obsolescent or entirely wanting. (77. // ; pi. 12, f. 21, 22). 



Limpia Canon, Texas, F. S. Earle and S. M. Tracy, April 25, 



1902, no. 251 ; this, the type specimen, is deposited in the her- 



