ADDENDA. 
In describing the Ulve at pages 8 and 9, I unintentionally omitted the 
species Ulva lactuca, so called from its fancied resemblance to a coss- 
lettuce. In early growth this plant is a long pear-shaped bag, which 
bursts at the top and splits down the sides, spreading out into segments of 
irregular shape and size. In structure this species differs from others of 
the genus, on which account, as observed by the late Mrs. Gatty, a sub- 
division of the Ulvew was proposed, under the name of ‘‘ Phycoceris,’’ to 
include Ulva latissima and U. linza. I prefer, however, to retain these 
plants in Ulva. The membranous fronds of these two species are double, 
though adhering closely together, while those of U. lactuca are composed 
of a single layer of cells. The mature frond of this plantis about 6in. 
long, and its colour is usually a pale green. Its place of growth is on 
rocks, shells, and also on other seaweeds, between tide-marks. 
The interesting species Polysiphonia divergens has been added to our 
British Marine Flora by Mrs. Merrifield, of Brighton, who identified it as 
such in a plant which was taken at Falmouth in 1861. It is a native of 
the South Atlantic, and is found at Cadiz, and also in the Adriatic. The 
plant is of small size, the fronds are very slender and much entangled ; in 
general aspect this rare species bears some resemblance to P. spinulosa. 
The siphons of the stem are six or seven, and are of nearly equal 
diameter. 
Fucus anceps is another rarity, which is taken, I believe, only on the 
west coast of Ireland. It was discovered by Harvey and Ward, and 
published as a new species by Mr. S. O. Gray in his “ British Seaweeds.”’ 
I have not seen this species in the growing state, but the dried specimen 
which I poszess, very strongly resembles the barren form of Fucus canali- 
culatus (Fig. 34), except that the fronds are not channelled and the ter- 
minal forks are not quite so blunt at the tips. 
Fig. 47 in this work, is an accurate representation of a young plant of 
Laminaria stenophylla, which Dr. Harvey has described as a var. of L. digi- 
tata (Fig. 46), but which is now regarded by Professor Agardhas a distinct 
species, and I think justly so. The chief points in which they differ are as 
follows. The stem in L. digitata is always round and roughish to the touch, 
especially in mature plants, when the periphery, or outer margin, may pro- 
x 
