DASYCLADEiE. 39 



thrice compounded and articulated ; being formed of two or three series of nearly 

 cylindrical cells, four to six times longer than broad, filled with dark green slimy endo- 

 chrome. The terminal cells are very obtuse. FrucUfication is formed at the axils of 

 the ramelli, where two or three supplementary cells are developed and become spherical 

 spora7i(/ia, by absorbing all the endochrome of the cells from which they spring, 

 and finally that of the whole frond. When ripe, these sporangia are membranous bags, 

 stufied with innumerable spherical spores. Colour, a deep grass-green. Substance, 

 soft and somewhat gelatinous. 



This species closely resembles, in habit and structure, D. clavceformis of the Medi- 

 terranean ; but the ramelli, even in the densest specimens, are much more distantly 

 placed than in that plant, and the apices (or terminal cells) of all the American indi- 

 viduals I have examined are perfectly blunt ; not mucronulate, as they are in D. clavce- 

 formis. If this distinction prove constant, the species will be sufiiciently characterised. 



Plate XLI. B. Fig. 1. Dasycladus occidentalis ; the normal form. Fig. 2. An 

 attenuated and depauperated variety ; both figures the natural size. Fig. 3. Trans- 

 verse section of the frond, showing a whorl of trichotomous ramelli. Fig. 4. Portion 

 of a fertile ramellus with sporangia. Fig. 5. A sporangium. Fig. 6. Spores from 

 the same ; all the latter figures magnified. 



III. ACETABULARIA. Lamour. 



Root scutate. Frond stipitate, umbrella-shaped, thinly incrusted with calcareous 

 matter. Stipes tubular, unicellular, cylindrical, when young emitting whorls of byssoid 

 fibrills at and below the summit ; when mature, crowned with a peltate disc, formed of 

 numerous radiating cuneiform cells. Cells of the disc at first containing granular 

 endochrome, which is afterwards changed into spherical spores. 



The two species which are included in this genus are among the most elegant and 

 singular of the Algae, resembling delicate fungi of tlie genw.?, Agaricus, more nearly than 

 any marine production. This is, however, descriptive only of the fully grown plant, 

 for in the young state, the peltate umbrella which crowns the stipes is not found. In 

 the youngest specimens which I have examined (represented at fig. 2 in our plate) 

 the upper part of the stipe is beset at sub-distant intervals with whorls of extremely 

 slender byssoid fibrills, above the last of which a young disc is commencing to be 

 formed. In older plants these fibrills drop away, and their position is indicated by an 

 annular row of holes, the tube being also swollen at each whorl, so as to appear jointed. 

 There are no septa, however, and the tube is continuous, at least to the base of the 

 young disc. "When the disc is further advanced, a dense pencil of fibres springs from 

 its centre, on its upper surface, or from what may be called its umbo, and which is 



