either undivided, but furnished with numerous alternate lateral branches ; or 
irregularly forked, and gradually dissipated in the bushy frond; branches 
long, simple or compound, much attenuated, more or less densely clothed 
with quadrifarious multifid branchlets, from one to two inches in length, 
alternately divided. Ramuli setaceous, acute, slightly tapering at the base. 
Tubercles abundant, forming a spherical swelling in the middle of the 
ramuli, one or move in each ramulus. Tetraspores oblong, divided by three 
transverse lines, into four parts, vertically immersed among the cells of the 
surface, dispersed through the smaller branches and ramuli. Substance 
cartilaginous, soft, imperfectly adhering to paper. Colour a dull purplish- 
pink, often pale; becoming much darker in drying. 
The genera Hypnea and Gracilaria are, as I have already 
noticed in the remarks under Plate LXV., very closely allied to 
each other, but the character derived from the tetraspores, there 
pointed out, will not serve to distinguish them, for I have 
since ascertained that annular tetraspores exist in most of the 
Gracilaria, as well as in Hypnea., If the two genera are to be 
maintained we must look for other distinctions, and these may be 
most readily found in the structure of the frond, the true Gra- 
cilarié having an axis composed of very large cells; the Hypnee 
having a more or less evident fibro-cellular axis, composed of 
minute, elongated cells. The calibre of this axis varies greatly 
in the different species, t1 some of which it exists like a thread ; 
in others, as in the present species, it is of great size, and the 
cells by which it is surrounded are of much smaller dimensions 
than in the typical 7. musciformis. Kiitzig, mdeed, forms a 
new genus, which he calls Cystocloniwm for our H. purpurascens. 
In this step I am not disposed to follow him, because it appears 
to me that the difference in structure is more one of degree, than 
of kind; and because the cirrhose habit of our var. 8. indicates 
a close relationship with the Hypnee, most of which produce 
similar tendrils. 
Hypnea purpurascens is among the commonest of our Algz, 
very variable in appearance, and very widely dispersed through 
the North Atlantic. If allowed to retain its place, it is the most 
northern example of the genus, none others bemg found north 
of the Mediterranean. 
Fig. 1. HypNea PURPURASCENS :—of the natural size. 2. Portion of a ramulus. 
3. Section of atuberele. 4. Tetraspores. 5. Cross section of the frond 
6. Longitudinal semi-section of the same :—all magnified. 
