No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 79 



others!); Denmark (Rosenvinge!); Helgoland (Kuckuck!); S. 

 Iceland (Strom felt, Jonsson!); the Faeroes (Simmons, Bor- 

 gesen!); Shetland (Borgesen); the Orkneys (Traill); the He- 

 brides (Stanford!) 1 ) The British Isles! The Atlantic coast of 

 France! Morocco: Tanger (Kuckuck!); the Adriatic: Brionic 

 Islands (Kuckuck!) 2 ) 



2. Phymatolithon Icevigatum Fosl. 



List of Lithoth. (1898), p. 8; Rev. Syst. Surv. Melob. (1900), p. 9; Litho 

 thamnion laevigatum Fosl. Norw. Lithoth. (1895), p. 139, t. 19, fig. 21—23. 



Syn : Lithothamnion laevigatum Heydr. Lithoth. Helgol. (1900), p. 76! Johns, 

 and Hensm. Irish. Corall. (1899), p. 29? 

 „ emboloides Heydr. 1. c. p. 74 ! 



Phymatolithon laevigatum Borg. Mar. Alg. Faeroes (1902), p. 4C0! Batt. 

 Cat. Brit. Alg. (1902), p. 98! De Toni, Syll. Alg. IV (!905), p. 1725. 

 Phymatolithon? emboloides De Toni 1. c. p. 1726. 



This species is distinguished for its thin and smooth crust, 

 which is often slightly shining, but particularly for its two-parted 

 sporangia. It cannot, however, with certainty be considered as 

 specifically distinct from Ph. polymorphum, which mostly shows 

 a surface more or less uneven, and bears four-parted sporangia. 

 The distinction depends on the stress to be laid on the partition 

 of the sporangia. Particularly in the southern part of their area 

 of distribution no line, as a general rule, can be drawn between 

 these two species either as to habit or as to structure. Thus on 

 the Atlantic coast of France, from where as yet Ph. Icevigatum 

 is not known, there occurs a form almost quite resembling the 



a ) According to a specimen in the British Museum under the name of Lithoth. 

 colliculosum. 



2 ) Among the specimens belonging to the group o[Ph.pohjmorphum — Icevigatum 

 which I have seen from the Atlantic coast of North America, only a few 

 belong to Ph. Icevigatum. The rest are sterile and resemble in habit partly 

 Ph. Icevigatum, partly Ph. polymorphum f. subloevis. A sterile specimen 

 from Magnolia (Herb. F a r 1 o w, II) attached to the hapters of Laminaria 

 digitaia recalls Lithoth. leave in habit, but seems most likely to represent 

 a form of Ph, polymorphum. Besides, I have seen a couple of specimens 

 from Greenland which resemble Ph. polymorphum in habit. They are, 

 however, sterile, and on the other hand also approach Lithoth. glaciale, 

 to which they are perhaps to be referred. 



