THE PERCY SLADEN TRUST EXPEDITION. 101 
elongated, 11-18 or up to 22, long, and 9-11 or up to 14 broad, partly and chiefly 
in the external layers often subsquarish, about 9 4 in diameter, here and there a little 
horizontally elongated. The cells, as a general rule, are rather thick-walled, in part 
forming layers of tissue rather strongly defined. 
The form parvula, which possibly represents the typical form of the species, bears in 
habit a considerable resemblance to small specimens of Lithophyllum racemus t. typica. 
It also approaches certain forms of Lithoth. fruticulosum, but the surface is smoother 
and, at any rate partly, feebly shining. The alga is freely developed on the bottom; but 
when it comes into contact with other calcareous algæ or other detached objects it partly 
develops a feeble crust, like several other species (cf. *Siboga' Exp. n. lxi. p. 41). 
Of the form crassa only a single specimen was found, which had also been lying loose 
at the bottom. In habit this form somewhat approaches Lithoth. brachycladum from the 
West Coast of Africa, Lithoth. validum from the Pacific Coast of North America, and 
Lithoth. floridanum from Florida, a group of species distinguished by coarse and short 
branches. Also as to structure it comes near to the species last mentioned. 
In this respect it also, as well as f. parvula, approaches Lithoth. indicum. The form 
in question bears a great resemblance in habit to certain forms of Arch. erythreum 
(cf. ‘Siboga’ Exp. n. lxi. pl. 5. figs. 8, 9). 
In both forms a partial decortication of the external layers of tissue of the 
branches occurs here and there rather closely recalling dissolved sori of sporangia of 
Archeolithothamnion. 
Only the single specimen of f. crassa bears a few conceptacles of sporangia. The 
conceptacles finally, at any rate now and then, become overgrown by new-formed tissue, 
and are in a median-vertical section rather flat-bottomed with corners in part scarcely 
rounded. A few specimens of f. parvula show scars from dissolved conceptacles. 
The species occurred at a depth of 55 fathoms, associated with Lithoth. australe and 
Squamariacea. 
Locality. Indian Ocean : Saya de Malha, No. C 15 (Stanley Gardiner). 
4. LITHOTHAMNION AUSTRALE, Fosl. 
Lithothamnion coralloides £, australis, Fosl. Norw. Lithoth., in Kgl. Norske Vidensk. Selsk. Skrift. 
1894 (1895), p. 92, ex parte; New or Crit. Lithoth., Z. c. 1899, n. 5 (1900), p. 8, figs. 6-7. 
Lithothamnion australe, Fosl. Rev. Syst. Surv. Melob., l. c. 1900, n. 5, p. 13; ‘Siboga’ Exp. n. lxi. 
livr. 18, p. 24, pl. 2. figs. 10-62. 
As to the rather uncertain circumscription of this species and its varying forms, I refer 
to my remarks in < Siboga' Exp. /. c. Also the specimens collected by Mr. Stanley 
Gardiner are sterile, Besides there are often developed thin erusts round specimens that 
Are wholly or partly dead, and it is impossible to decide whether these crusts are new 
layers of accretion issuing from the part of the alga still living or, when the specimen 
18 wholly dead, may represent young crusts of the same or another species. ds 
The form occurring at Saya de Malha is most nearly connected with f. ¢walensis, in 
part, however, coarser than typical specimens of that form. There are also some 
finely branching specimens which very nearly approach f. minutula and are perhaps 
SECOND SERIES.— BOTANY, VOL. VII. - 
