184 PERCY SLADEN TRUST EXPEDITION 
numbers in typical specimens from Australia, and less well developed and scanty in 
specimens from Providence. They diverge from the same organs in Lithothamnion 
Jruticulosum by being almost superficial and conic or almost conic, always more pointed 
than in the latter species. They are finally quite dissolved, and thus they are not over- 
grown by new-formed tissue, as is often the case in Lithoth. fruticulosum. Accordingly 
I must consider the Indian and Pacific forms as independent species. 
In the area in question Lithoth. indicum occurs in comparatively great depth. But it 
is generally smaller and not so vigorous and well developed as, e. g., in Port Philip Bay, on 
the south coast of Australia, where it seems to be abundant in a depth of 2-5 fathoms. 
Thus at Cargados Carajos and at Providence it attains to a size of only about 4 cm. 
Ifere it bears sporangia in the months of August and September. In the former of 
these localities it occurs scantily in a depth of 30 fathoms, partly associated with Lithoth. 
australe, but particularly with rather numerous indeterminable and mostly dead calcareous 
algee, in part attached to shells of mussels. At Providence it also occurs in a depth of 
about 30 fathoms and in rather large numbers. Here it has also been picked up from a 
depth of 50-78 fathoms, though only a few certain specimens together with some 
uncertain and indeterminable ones. From Amirante has been brought home an uncer- 
tain specimen, and from the Seychelles have been brought home two specimens not 
well developed. 
Localities. Indian Ocean: Cargados Carajos, No. B 8 (30 fathoms), No. B 9 
(30 fathoms), No. B 18 (80 fathoms), No. B 14 (80 fathoms); Providence, No. D 3 
(29 fathoms), No. D 4 (50-78 fathoms), No. D 24 (30 fathoms); Amirante, No. E 13 
(20-25 fathoms), uncertain; the Seychelles, No. F 2 (31 fathoms) (Stanley Gardiner). 
Area. Mauritius; the Maldives; the south coast of Australia (Port Philip Bay); and 
several places in the Pacific Ocean, particularly the Malay Archipelago. 
3. Lithothamnion gibbosum, Fos. 
Kgl. Norske Vidensk. Selsk. Skrift. 1906, n. 8 (1907), p. 7 (in Norwegian). 
Thallus freely developed at the bottom, roundish, 1°5—4 cm. in diameter; branches 
subdichotomous, radiating from the centre, short, frequently crowded, partly rather 
anastomosing, partly not, subfastigiate, upper parts irregularly roundish-thickened or 
subcompressed, knotty, 2-7 mm. thick, smooth, and feebly shining; conceptacles of 
sporangia convex, but little prominent, 400-650 » in diameter ; sporangia unknown. 
f. parvula, Fosl. 
1 Upto 
Thallus 1°5-2 em. in diameter, branches 2~3 mm. thick. 
f. erassa, Fosl. 
a 
Thallus 3-4 em. in diameter, branches 4—7 mm. thick. 
In a median section of a branch the medullar hypothallic cells are mostly 18-25 » or 
up to about 30 long, and 11 (9)-14, broad. The perithallic cells are partly vertically 
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