MAEINE ALGiE OF THE ' SEALAEK ' EXPEDITION. 133 



Amphisbetema, n. g. 



Thallus constat e pede crasso rhizomatoideo, unde nascuntur axes erecti, corticati, 

 regulariter sympodii modo compositi e ramis incremento finito conspicue mono- 

 podialibus dorso-veutraliter crescentibus. 



50-veutraliter crescentibus. Axis constat ex una ccllula centrali et 

 sex cellulis pericentralibus, tribus aut quatuor ordinibiis cellularum longitu- 

 dine celMse primariae pericentralium cinctis ; quos ordincs stratum corticalc 

 crassum e cellulis parencbymaticis fissis compositum cifig'it. Cystocarpia et 

 antheridia ignota. Stiebidia. sporis verticillatis, seque ac in Basija non omnirio 

 cellulis corticalibus obtectis. 



1. Amphisbetema indica (J. Ag.). (Plate 13. fig. 24; Plate 14. fig. 31, and text-fig.) 



I)asya indica, J. Agardh, Till Alg. Syst. xi. 1890, p. 111. 



Diagnosis tbe same as tliat of genus. 



Aldabra, reef, Passi Honakan, outside ; dry specimens. 



DistributAon, Diego Garcia. 



Tbe alga for wbicb I propose tbe generic name of Ampldshelema was described in 

 1890 by J. Agardh under tbe name of JJasija indica ; tbe structure of tbe sticbidia, 

 almost identical witli tbat of Dasya, probably induced tbis eminent algologist to 

 describe tbe plant under tbat name, for be was quite cognisant of tbe differences in 

 ramification between bis alo-a and otber Dasyce. In De Toni's 'Sylloge Algaram,* 



iv. p. 1146, 1903, Basija indica bas received tbe name of Wilsoncea (?) indica. 



I found tbis alga in tbe collection of Mr. Stanley Gardiner, and tbrougb tbe kindness 

 of Sir David Prain I was able to compare it with autbcntic material from Diego Garcia, 

 now preserved in tbe Herbarium at Kew, and I wish to express jny best thanks to him 

 for so liberally placing tbis material at my disposal. The study of tbe type-specimens 

 enabled me to identify my barren material from Aldabra. This differs only from the 

 type in being a little stronger; the algae 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, 

 attainini? a hei-ht of 8-9 cm., with distichous bilateral branches. These main axes 



O "■ "^"O 



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, as 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 tbe base, and all tbe 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 ihey 

 ultimately take their bilateral position. The branches of the second order have the 

 same ramification as the primary ones and are alwc.ys 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, 



