Howe anpD UNpERWoop: THE GENUS RIELLA 221 
divided by transverse walls into a single row of several cells, three 
or four of the terminal of which are then divided by median lon- 
gitudinal walls. This divided terminal portion by growth and 
multiplication of its cells becomes ovate or spatulate in outline. 
In the latest stage that we have been able to see, one somewhat 
more advanced than that represented in our f. 27, the whole body 
still consists of only one layer of cells. . 22 shows in edgewise 
view the same plant that is shown in f 27. A root-hair is sent 
out from the spore soon after the emergence of the germ-tubes. 
A second species of Rze//a, apparently new, from the Canary 
Islands, has come to our attention; this we would describe as 
follows : 
Riella affinis sp. nov. 
Apparently erect or ascending, becoming prostrate on the sub- 
sidence of the water, 6-15 mm. high, densely caespitose, simple or 
sparingly furcate: axis flattened, 0.1-0.4 mm. wide, mostly thin 
and flaccid, radicelliferous at base: wing 1-3 mm. broad, rounded 
or obtusely pointed at apex and falciform, deeply lobed; cells 
near the axis 45-60 in diameter, those near the margin about 
304: scales usually inconspicuous, 0.2—-0.5 mm. long, linguiform, 
lanceolate, or linear, obtuse or acute: monoicous: antheridia 
solitary or in groups of 2-7 in more or less profound marginal 
sinuses: sporogonia mostly 3-10: involucres ovoid, 8-winged, 
1.4-2 mm. long, I-1.5 mm. wide (incl. wings), much contracted 
and often subacute at mouth; wings o.I-0.2 mm, broad, with 
undulate-sinuate or subentire margin: capsule subglobose, 0.8—1 
mm. in diameter, seta 0.1I-0.2 mm. long: spores brown, 85-— 
120 in maximum diameter (spines included) ; outer face densely 
covered with spines 6-15 long, their apices mostly truncate, often 
slightly dilated, occasionally emarginate-bifid, rarely acute, the 
supporting basal membranes sometimes almost deficient but com- 
monly forming a few imperfect areolae ; inner faces with mostly 
truncate or obtuse spines or warts 3-6 high, basal membranes 
wanting. (f7. 12. f. 23-306.) 
On the bank of a reservoir, Tafira, Grand Canary, June, 1897, 
O. F. Cook (no. 729). We are informed by the collector that the 
specimens were found partly submerged and partly exposed on a 
sloping bank. 
Riella affinis is allied to the Algerian R. Cossoniana Trabut and 
the central Asian R. Pau/senii Porsild, but differs from both in 
being monoicous and in the much longer spines of the larger 
