14 RHOpOMELACE^. v. 



Northern Ocean, our American one being common to the north of Europe, and the 

 other known species to the north-eastern shores of Asia. 



1. Odo7ithalia dentata, Lyngb.; decompoundly pinnate ; branches oblong, deeply 

 pinnatifid or bipinnatifid ; lacinite alternate, linear, sharply inciso-dentate toward 

 their truncated extremities ; conceptacles and stichidia both clustered, axillary. 

 Harv. Phyc. Brit. t. 34 {colour incorrect). KUtz. Sp. Alg. p. 846. Fucus dmtatus, 

 Linn. Turn. Hist. t. 13. E. Bot. t. 1241. 



Hab. On rocks and stones in deep water. " Shores of America," Gmelin. Dredg- 

 ed in Halifax Harbour, W. H. H. Arctic Coast, Mr. Seeman. (v. v.) 



Fronds 3-12 (in the Halifax specimens 4-5) inches long, decompoundly pinnati- 

 fid, the main divisions irregular, the secondary and subsequent regularly alter- 

 nated, and erecto-patent. The main branches are evidently ribbed towards the 

 base, where the marginal wing is narrow and frequently defective, and become less 

 obviously ribbed, broader, flatter and thinner upwards. The secondary branches 

 have an oblong or lanceolate or sometimes a flabelliform outline and are alternately 

 pinnatifid ; the lowest laciniaj short, broadly subulate, tooth-like, the upper gra- 

 dually larger and altei'nately inciso-dentate or again pinnatifid. In the specimens 

 with flabelliform branches the upper laciniae are proportionably much longer and 

 more compound, all their divisions spreading. Axils very obtuse. Apices acute. 

 The internal structure is dense, the substance composed of innumerable small, 

 polygonal cells, closely packed together ; those of the surface exceedingly minute. 

 Fruit (which I have not seen on American specimens) borne on little marginal 

 processes either in or near the axils of the lacinite ; both conceptacles and stichidia 

 tufted. Colour, when growing, a clear, full, blood-red, becoming darker and 

 changing either to vinous purple or to brown red ; when dried the tips sometimes 

 assume a pinky tint. 



The American specimens are smaller and narrower than the generality of those 

 of British growth, but I can find no distinctive character, and have seen some from 

 Orkney equally narrow. The 0. angustifolia, Suhr, judging from a specimen in 

 Herb. T. C. D., is a different species, seemingly the same as 0. Kamtchatica, Rupr. 

 The colour of the plate given in Phycologia Britannica, copied from a dried 

 specimen, is very incorrect ; when growing, this plant is of a clear, translucent red. 



III. ALSIDIUM, Ag. 



Frond filiform or compressed, cartilaginous, pinnately or irregularly de- 

 compound, opaque, coated with small polygonal, irregularly placed cells; axis 



