WEBER-VAN BOSSE—MARINE ALG 297 
AMPHISBETEMA, 0. g. 
Thallus constat e pede crasso rhizomatoideo, unde nascuntur axes erecti, corticati, 
regulariter sympodii modo compositi e ramis incremento finito conspicue mono- 
podialibus dorso-ventraliter crescentibus. Axis constat ex una cellula centrali et 
sex cellulis pericentralibus, tribus aut quatuor ordinibus cellularum longitu- 
dine cellule primariz pericentralium cinctis; quos ordines stratum corticale 
erassum e cellulis parenchymaticis fissis compositum cingit. Cystocarpia et 
-antheridia ignota. Stichidia sporis verticillatis, eque ac in Dasya non omnino 
cellulis corticalibus obtectis. 
1. AMPHISBETEMA INDICA (J. Ag.). (Plate 17. fig. 24; Plate 18. fig. 34, and text-fig.) 
Dasya indica, J. Agardh, Till Alg. Syst. xi. 1890, p. 111. 
Diagnosis the same as that of genus. 
Aldabra, reef, Passe Houareau, outside; dry specimens. 
Distribution. Diego Garcia. 
The alga for which I propose the generic name of Amphisbetema was described in 
1890 by J. Agardh under the name of Dasya indica; the structure of the stichidia, 
almost identical with that of Dasya, probably induced this eminent algologist to 
describe the plant under that name, for he was quite cognisant of the differences in 
ramification between his alga and other Dasye. In De Toni’s ‘“‘Sylloge Algarum,” 
iv. p. 1146, 1908, Dasya indica has received the name of Wilsonea (?) indica. 
I found this alga in the collection of Mr. Stanley Gardiner, and through the kindness 
of Sir David Prain I was able to compare it with authentic material from Diego Garcia, 
now preserved in the Herbarium at Kew, and I wish to express my best thanks to him 
for so liberally placing this material at my disposal. The study of the tvpe-specimens 
enabled me to identify my barren material from Aldabra. This differs only from the 
type in being a little stronger; the alge from Diego Garcia bear stichidia with 
tetrasporangia, a fact which may account for their being more slender. 
Amphisbetema has a strong rhizome-like base from which arise erect main axes, 
attaining a height of 8-9 cm., with distichous bilateral branches. These main axes 
are composed of branches or shoots of definite growth, succeeding each other at a 
distance of six segments to be then displaced by their own first branch. The branches 
have, so far as I could make out, monopodial growth; sympodial growth sets in only 
when each in turn is pushed aside. All the branches have a dorsi-ventral organization ; 
their first branch of the second order is always inserted at a distance of six segments 
from the base, and all the succeeding ones at a distance of two segments; they stand 
in two rows on the ventral side of the branch, and only by subsequent growth do they 
ultimately take their bilateral position. The branches of the second order have the 
same ramification as the primary ones and are always turned to one side; each 
principal branch carries as a rule six pairs of branches of the second order; but the 
nearer to the apex the less do they develop. 
After the formation of these six pairs of branches, the vigour of each mother- 
branch seems to be exhausted. At a distance of three or four cells from the apex, 
