This elegant plant, which was formerly included in the genus 

 Sporochnus, was, nearly at the same time, by M. Duby in France, 

 and by the Rev. M. J. Berkeley in this country, proposed as the 

 type of a distinct genus. M. Duby's name, having the priority 

 of a few months, is here adopted. Of the propriety of constituting 

 a new genus in this instance, there can be no question, both the 

 structure of the frond, and the nature of the fructification being 

 very unlike that of the JSporoc/mi. There is, indeed, a much 

 closer connection with Desmarestia, both in habit and in struc- 

 ture, and it is very probable that the fruit of Desmarestia may 

 prove to be analogous to that of the present genus. At a first 

 glance the difference in the structure of the frond between Des- 

 marestia and Arthrocladia appears considerable, but a closer ex- 

 amination removes much of the dissimilarity. A jointed tube 

 runs through the centre of both fronds ; in the Desmarestia, in 

 the form of a slender filament ; in the Arthrocladia of a wide 

 tube. The confervoid filaments are of the same nature in both 

 genera, and the branching of the fronds identical. The great 

 difference lies in the comparative density of structure. 



Dr. Greville mentions that Mr. Hasell, the discoverer of A. 

 villosa in Scotland, observed that " fresh specimens when spread 

 upon paper, rendered it transparent, as if it had been touched 

 with oil ; but in a very short time the transparency quite disap- 

 peared." This property is not peculiar to this species, but exists 

 also in young specimens of Desmarestia ligulata, and D. kerbacea, 

 and perhaps of others of the family, and affords another evidence 

 of the strong natural connection of these plants. Another com- 

 mon point of resemblance consists in their soon becoming flaccid 

 and changing to a verdigris green colour on exposure to the 

 atmosphere, and then causing the rapid decomposition of any 

 other delicate Alga in contact with them. This is common to 

 all the Sporoc/moidete. 



Fig. 1. Arthrocladia villosa : — natural size. 2. Part of a branch, showing 

 a whorl of filaments. 3. Longitudinal section of the frond. 4. A trans- 

 verse section of the same. 5. Pods of fructification: — more or less highly 



