THE PERCY SLADEN TRUST EXPEDITION. 105 
Subgenus PoRorrrHoN, Fosl. 
11. LITHOPHYLLUM ONKODES, Heydr. 
Ber. der Deutsch. bot. Ges. xv. (1897) p. 410. 
Lithothamnion onkodes, Heydr. Neue Kalkalg. (1897) p. 6, partim (Bibl. Bot. vii. Heft 41). 
This no doubt important reef-builder occurs in the Chagos Archipelago and at Coetivy 
in an unusually vigorously developed form. It forms massive and more or less uneven 
crusts, and probably covers the reefs to a considerable extent. It often also incrusts 
other objects and on the whole rather varies in shape. Thus it sometimes even 
forms small cap-shaped coverings on the apices of branches of corals. The species 
is generally of very firm consistency, and therefore rather heavy proportionately 
to the size. 
At Salomon Atoll it was also picked up from a depth of 10-14 fathoms in the lagoon, 
inerusting shells of mussels or pieces of coral, but the specimens, however, are small and 
feebly developed. It is not known whether specimens vigorously developed occur at this 
depth. 
In Lithoth. Mald. & Laccad. p. 468, I mentioned that in a vertical section of some 
of the crusts “the cells are here and there larger than is generally found, more regular, 
and with their longest diameter in a vertical direction.” This is also in part the case 
with the specimens in hand. In several of the most vigorously developed ones the cells 
also form here and there rather distinct layers of tissue, sometimes even irregularly 
alternating short and long cells. Frequently small groups of enlarged cells are 
numerous. 
Old specimens of this species are mostly sterile, but younger ones are provided with 
reproduetive organs in the months of May and June at Salomon and Egmont Atolls, 
and at Coetivy in September. 
. Localities. Chagos Archipelago: Salomon Atoll, reef, and lagoon 10-14 fathoms; 
Egmont Atoll, reef ; Coetivy, W. reef (Stanley Gardiner). 
Area, The Mauritius; the Maldives and Laccadives ; Ceylon; and widely dispersed in 
the Pacific Ocean. 
12, LITHOPHYLLUM CRAsPEDIUM, Fosl. : 
New or Crit, Calc. Alg., in Kgl. Norske Vidensk. Selsk. Skrift. 1899, n. 5 (1900), p. 26 ; Lithoth. 
in Gardiner, Mald. & Laccad. i. p. 466, pl. 25. figs. 1, 2. 
This species also appears to be an important reef-builder, forming, when most 
vigorously developed, sometimes almost columnar masses with coarse branches. The 
specimens brought home partly belong to the typical form of the species with branches 
almost terete, but rather anastomosing, with transitions to f. compressa, partly to 
f. abbreviata with smaller and shorter branches. s 
As is remarked below under Lithoph. Gardineri, the latter and Lithoph. craspedium 
are closely connected with each other, though Lithoph. craspedium is in general much 
Coarser and a more vigorously developed alga. There are, however, cases in which they 
are with certainty distinguishable only by their anatomic structure. In Lithoph. 
Gardineri, in a median section of a branch, the medullar hypothallic cells prove to 
