No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 75 



or but scarcely so and settles a little towards maturity, then, or 

 particularly when being on the state of decomposition, to the 

 naked eye rather resembling the conceptacles of sporangia. Those 

 of antheridia are of about the same shape as the conceptacles of 

 cystocarps, but only 80 — 110 \>. in diameter. 



As to host plant, the species particularly occurs on different 

 Floridese, e. g. Furcellaria, Phyllophora, Rhodymenia, Chondrus, 

 Gigartina, Rytiphlea and some others. It is now and then met 

 with also on Cladophora, and as a rare exception it even occurs 

 on the stem of Laminaria digitata (at Roundstone on the west 

 coast of Ireland !). The species, on the other hand, seems never 

 to occur on Zostera. The statement of some writers, that it is 

 found on this plant, — as far as I have hitherto seen — is owing 

 to confusion with Melobesia Lejolisii. It has its greatest occur- 

 rence in northern areas, — as far as is hitherto known, in the 

 tract from southern Norway to Ireland. The alga is to be found 

 on the said host plants partly in rock-pools in the lower part of 

 the litoral region, partly and especially in the sublitoral region and 

 here descending to a depth of about 8 — 10 fathoms. It is nearly 

 always richly fructiferous. 



Area: Norway: South-west and south coast (!). Sweden: 

 West coast! Denmark! British Islands ! Atlantic coast of France! 

 The Mediterranean! The Adriatic! Cape of Good Hope (Harvey, 

 Tyson!); Australia (according to Rosanoff). 



Phymatolithon Fosl. 



Syst. Surv. Lithoth. (1898), p. 4; De Toni, Syll. Alg. IV (1905), p. 1724; 

 Eleutherospora Hey dr. Lithoth. Helgol. (1900), p. 64. 1 ) 



Subgen. Euphymatolithon Fosl. mscr. 

 1. Phymatolithon polymorphum (L.) Fosl. 



Syst. Surv. Lithoth. (1898), p. 4; Millepora polymorpha L. Syst. Nat. ed. 12 

 (1758), p. 1285, partim. 



r ) I now place Phymatolithon after Lithothamnion, as it in reproductive organs 

 somewhat approaches Archceolithothamnion. Cp. Siboga Exp. LXI, p. 10. 



