32 



colour. The pinnae are of a lighter colour, alternate, closely 

 arranged in pairs on each internode, and vary from one eighth 

 to two thirds of an inch in length. The cells are uniserial, 

 crowded, and cup-shaped ; the apertures, patulous, deeply 

 notched with about eight indentations, and at a short distance 

 beneath the rim is a stout rounded spine. Each cell rests on 

 a separate internode of the pinna. The vesicles, though liable 

 to much variation, have all a very peculiar and characteristic 

 appearance, resembling minute barrels, embraced with from 

 five to nine serrated ribs. They are quite transparent when 

 living, allowing their irregularly shaped ova to be seen 

 throngh the sides; but when dry, they become opaque and of 

 a pearly hue. They are generally attached to the pinnae 

 throughout their length by a dorsal band. This band is 

 sometimes free and arched, and the vesicles attached only at 

 the extremities. The circular ribs have sometimes only one 

 prominent serrated rim and at others two. 



The description of the cells given above, is taken from such 

 specimens as most nearly approach to the descriptions and 

 figures of authors, more especially of Ellis and Johnston. 

 But there are variations from this standard, too remarkable to 

 be passed unnoticed. In no specimen have I seen the cells so 

 crowded as in Johnston's figure; Ellis' at pi. 7, more closely 

 approaches to the mode of distribution observed in Cornish 

 specimens, but he bas omitted the sub-marginal spine ; the 

 artist having drawn from an oblique back view, instead of a 

 lateral one, as he himself remarks. In one variety the cells 

 are deeply tubular; the mouth is deeply indented with five, 

 six, or seven teeth; the spine beneath the aperture, is stout, 

 and in those cells on the lower pinnae, frequently twice as 

 long as the diameter of the cell. Above each aperture and 

 attached to the upper portion of ec>ch internode, is a short 

 tubular process which lies across the mouth of the cell ; it 

 has a rounded termination, with a sublerminal opening on the 

 upper surface, very closely resembling what is observed in 

 the Cellaria Bursaria or shepherd's purse Coralline : a form 

 more clearly observable in the dried than in the living state. 

 There is also a minute variety growing on the smaller fuci, 

 stones and shells about low water mark, which rarely exceeds 

 half an inch in height; in which, the pinnae are very slender 

 and long, equalling in length, the height of the stem. It re- 

 sembles the common specimens in every respect, except that 

 every part is more minute. Though these are here called 

 varieties, y et one of them may probably prove a distinct species. 



The figure of this species, illustrating this essay, is of the 

 natural size of a very fine specimen from deep water. The 

 draughtsman has omitted the cells on a portion of the plume 

 on the right side. 



