lines along the margin. Occasionally spines and filaments are to be found 

 at the same time, the former being slender and weak. Substance cartila- 

 ginous when young ; very rigid when old. Colour, at first, pale greenish 

 olive, finally, foxy brown. 



At different stages of its growth this plant presents such oppo- 

 site appearances, that a young botanist may readily mistake, for 

 two species, forms which depend entirely on age, and which have 

 deceived even Linnaeus himself. When young, the whole frond 

 is of a tender substance, bright green colour, and beautifully 

 fringed with filaments ; when old, it is coarse, brown, naked, 

 and thorny. In plants of the second year, such as our figure 

 represents, these characters are often found combined in the 

 same specimen, in which the older parts of the frond are naked 

 and spiny, the younger shoots being green and clothed with 

 pencilled filaments. No fructification has yet been observed on 

 this, or any other, species of Desmarestia. 



In the Southern Ocean a closely allied species was found at 

 Cockburn Island, lat. 64° 13' S., by the officers of the 'Erebus ' 

 and ' Terror', nearly at the southern limit at which they observed 

 a marine vegetation. It appears to be identical with D. media, 

 Ag., a species originally found at Unalascha, in Russian America, 

 and differs from D. aculeata in having the branches generally 

 opposite or nearly so. It, indeed, presents characters almost 

 exactly intermediate between Dic/doria viridis and D. aculeata ; 

 so much so, that I do not think the genus Dichloria can be 

 retained as distinct from Desmarestia, notwithstanding the ab- 

 sence of confervoid filaments. 



Pig. 1. Desmarestia aculeata; a small plant : — natural size. 2. One of the 

 byssoid fibres. 3. Transverse section of the frond. 4. Longitudinal semi- 

 section of the same : — magnified. 



