221 Howe and Underwood : The Genus Riella 



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. 21, the whole body 

 still consists of only one layer of cells. F. 22 shows in edgewise 

 view the same plant that is shown in /. 21. A root-hair is sent 

 out from the spore soon after the emergence of the germ-tubes. 

 A second species of Riella, 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, 6-1 5 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 /i in diameter, those near the margin about 

 30// : 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, 1-1.5 mm. wide (inch wings), much contracted 

 and often subacute at mouth; wings 0.1-O.2 mm. broad, with 

 undulate-sinuate or subentire margin: capsule subglobose, 0.8-1 

 mm. in diameter, seta 0.1-0.2 mm. long: spores brown, 85— 

 \20 fi 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. {PI. 12. f. 23-36) 



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. Paulsenii Porsild, but differs from both in 

 being monoicous and in the much longer spines of the larger 



