SIPHONACEiE. 
25 
Fronds solitary, erect, with a cuneiform stipes composed of several confluent articu- 
lations and dividing at the summit into numerous branches, which soon again subdivide 
in a di-poly-chotomous manner, all the branches lying in one plane, so as to form a 
flabelliform frond. The articulations are all compressed, the middle ones more or less 
cuneate ; the upper usually tridentate or three-fingered, and frequently bearing articu- 
lations from the summit of each lobe. Colour rather a bright green. Calcareous 
incrustation thin. 
This is nearly related to H. incrassata , and perhaps only a variety. But the crust 
is not so dense, and the distinctly three-lobed upper articulations are characteristic. 
Ellis’s figure correctly represents a small branch. 
Plate XLIY. C. Halimeda tridens ; the natural size. 
4. Halimeda tuna , Lamour. ; frond much branched, diffuse, di-trichotomous ; articu- 
lations flat, thin, very broad, roundish or somewhat reniform, mostly entire ; the middle 
ones sometimes cuneate. Lamour. Pol. Flex. p. 309, t. 11 .jig. 8. Dne. Cor. p. 91- 
Kiitz. Sp. Alg. p. 504. Corallina Tuna , Ell. and Sol. tab. 20, Jig. e. Hal. platy- 
disca , Dne. ? p. 90. (Tab. XL. A.) 
Hab. Key West, W. H. H. Key Biscay ne, Prof. Tuomey. (v. v.) 
Root deeply descending. Stipes scarcely any, consisting of a single, cuneate or 
flabelliform articulation, which is sometimes more than an inch across, from the upper 
margin of which spring numerous other articulations, forming the bases of so many 
irregularly dichotomous branches. The articulations vary much in form and size. 
Their usual shape is roundish or sub-reniform, and they are from half to § inch broad, 
quite flat, smooth, and thinner than in most species. They are joined together by very 
much constricted nodes, and are usually broader than their length. In some of my 
specimens, however, some of the medial articulations are narrow-cuneate or almost 
clavate. There is less incrustation in this species than in most ; the colour is a bright 
green, and the substance somewhat flexible. 
The original H. Tuna is a native of the Mediterranean ; and possibly the plant now 
described may be referable to H. platydisca, Dne., but some of my Key West specimens 
so closely resemble what I have received from the Mediterranean, that, habitat apart, I 
cannot find a character to distinguish them. Others are certainly of larger size, with 
more discoid articulations. If, however, every slight variation in form and size is to 
be made the foundation of a new species, and dignified with a special description and 
name, the number of species to be established would only be limited by the num- 
ber of specimens examined ; for scarcely two are to be found identical at all points. 
Plate XL. A. Halimeda Tuna , the natural size. 
E 
