DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHIATE POLYPI. 405 
very short (fig. 3. a 4.). (It is possible that this notched margin may be formed by 
the extremities of short and broad setae, but this was not determined.) The cells 
spring from the sides and upper surface of the stem, and turn upwards as in Bnwer- 
bankia. They are set at some distance apart. 
The gemmae exhibit the same process of growth as in other cases, and are scattered 
irregularly amongst the larger cells (fig. 3.). 
PLATE XXV. and XXVI. 
Halodactylus diaphanus, Mihi # . 
Syn. Alcyonium seu Fucus nodosus et spongiosus, Ellis, Cor., p. 102. pi. xxxii. 
fig. d. D. 
Alcyonium gelatinosum , Linn., Gmel., p. 3814. No. 11 . Lamx. Polyp, flex., 
p. 350. No. 495. Mull. Zool. Dan. iv. p. 30. t. cxlvii. f. 1 — 4. Flem. 
Brit. Anim. p. 517- gen. xl. 86. 
Alcyonidium diaplianum , Lamx. Gen. Thalass. p. 7L t. 7- f. 4. Hooker, Flora 
Scotica, part II. p. 75* London Encyc. of Plants, 1829, p. 928. 
Ulva diaphana, Hudson, Flor. Angl., vol. iii. p. 570. Sowerb. Engl. Bot. 
t. 263. 
Extremely common on the Sheppy coast, especially after a gale, when it is cast up 
in immense quantities, and is found attached to loose stones and shells, in the form of 
soft, flexible, finger-like processes of very irregular figure, being rounded and smooth 
upon the surface, or flattened, nodulated and branched, sometimes attaining the 
length of two or three feet, but generally about six inches long. The animals are, 
however, so small that such specimens must contain many millions of them. When 
a portion of this is placed in a trough of sea-water, the little animals are seen quickly 
to emerge in such numbers as to cover its surface with a coating as it were of the 
finest down ; and they are so closely set that there seems to be hardly room for their 
several operations (fig. 1.). In this state it is scarcely possible to make any observa- 
tions upon them, but when a few only are projecting they become from their extreme 
delicacy and transparency peculiarly favourable subjects for examination. On this 
account, and also from the length of time that they may be kept in vigour, I have 
been enabled to prosecute the inquiry further than other specimens enabled me to do. 
Plate XXVI. fig. 7- The tentacula are sixteen in number, (occasionally fifteen)! 
fully two-thirds the length of the body of the animal, and extremely slender and 
* aXs et SaurvX os. The confusion and doubt which have so long pervaded the very ill-defined genera Alcyo- 
nium and Alcyonidium appear likely to be dispelled only by beginning de novo, and adopting a new name in 
conjunction with characters sufficiently definite to preclude all probability of further error. I have therefore 
renamed the present species as indicative of a new genus, with which other species will probably he found, 
upon a minute examination of their intimate structure, to possess congeneric affinities. 
f Fleming, Lamouroux and others appear to be in error in stating them to be twelve. 
3 g 2 
