397 
though I think the amount of thickening of the basal cells de- 
pends on their position, the upper ones from the same plants being 
quite hyaline and smooth at base, with thin walls. Even the 
shape of the cells is variable, for they may be oblong and parallel 
with the vein, or they may be rhomboidal and oblique. 
In reply to a recent letter of mine, Dr. Venturi says, concern- 
ing O. sordidum, that “the group of O. affine differs from that of 
‘O. arcticum only in the position and form of the papilla on the 
Surface of the teeth. These, like O. affine, have the papilla more 
dispersed and irregular and occasionally truncate and reduced to 
intersecting lines, whereas in the group of O. arcticum the papille 
are smaller, more dense, and distinctly elevated. O. sordidum has 
the papille corresponding to the group of O. arcticum, not only in 
your specimen, but in all the others which I have examined. 
That would not prevent it, however, from being otherwise closely 
allied to O. affine.” 
OrtHorricuium Lyetiu, Hook. &- Tayl. Musc. Brit. i. 29 t. 22 
(1818). 
O. papillosum, Hpe. Linnza, xiv. 458 (1860). 
O. Pacificum, Hpe. ms. in Herb. Brit. Museum. 
O. Sullivantii, Bauer; Austin in Bull. Torr. Bot. Club, vi. 343 
(1879) (?). 
O. Pringlei, Miiller, Bull. Torr. Bot. Club, xiii, 121 (1886). 
QO. strictum, Vent. (sub-species nova) Bot. Cent. xliv. 419 
(1890). 
Such is the published synomymy of this species. Several 
times it has excited my curiosity, and the following notes and 
comparisons have been made. Two authentic specimens of O. 
Lyellii collected by Greville in Scotland, in Dr. Torrey’s Her- 
barium are dark green plants with the leaves erect or secund, not 
crisped, though occasionally recurved or subsquarrose. They are 
plentifully sprinkled with brown propagula, and are distinctly 
Papillose on both surfaces, or, as Braithwaite describes it, “ with 
Prominent conical papilla.” He says in a foot-note that Dr. 
Spruce found a marked form by the Ouse, near York, in 1843, 
with rigid closely appressed leaves. 
O. papillosum, Hpe. 1. c. (O. Lyellii, var. S. & L. Musci Bor. Am. 
Ed. ii. no. 185 Senet 
