310 PROFESSORS EDWARD FORBES AND J. GOODSIR ON SOME 
In the synopsis of the genera of zoophytes, by Minne Epwarps and Haine, 
the genus Sarcodictyon is placed in the family Cornularine, among the Alcy- 
onaria. Wecan hardly assent to its removal from the immediate neighbourhood 
of Alcyonium, for it differs merely in the stoloniferous method of growth. The 
new species now announced, goes far to confirm our view of its affinities. This 
genus may be said to bear much the same relation to Alcyoniwm, which our new 
genus Syntethys (among the Ascidians) bears to Clavelina. 
Arachnactis albida. Sars.—In the first part of the very beautiful and valu- 
able work by M. Sars, entitled “ Fauna Littoralis Norvegiz,” published at Chris- 
tiania in 1846, a new genus and species of Helianthoid zoophytes is described at 
length, and figured in detail, under the name of Arachnactis albida. 
In the “ Travels in Lycia,” by Professor E. Forpes and Captain Spratt, R.N., 
published in 1847, a swimming Actinea is noticed and figured from the Egean. 
This was clearly a species of Avachnactis. 
When Dr Batrour visited the Island of Lewis with his pupils in August 1841, 
they procured a number of mutilated specimens of a radiate animal found floating 
in the Minch. These were too imperfect for determination at the time. This year, 
however, we have discovered a species of Arachnactis evidently identical with 
the Norwegian one in the Minch, and the remains of Dr BAaLrour’s animal have 
proved identical with it. 
The definition of the genus given by Sars is,—‘“ Animal liberum, molle, 
natans; corpus breviter cylindricum, parvum, basi rotundata, disco suctorio 
carente; os seriebus tentaculorum non retractilium duabus circumdatum, exte- 
rioribus longissimis, interioribus brevibus.” 
The number of the larger tentacula were eight to ten, of the smaller, accord- 
ing to Sars, twelve; we have observed them as many as sixteen. The shape of 
the body is pyriform ; its colour dusky white, tinged with tawny. The outer 
tentacula are very long, tawny and white; the inner, much shorter. The length 
of the body is about one inch. The outer tentacula can be extended to three or 
four times the length of the body. The creature swims freely, and habitually in 
the manner of a medusa. 
There is a point, however, of consequence which Sars did not observe, it can 
convert its posterior extremity into a suctorial disk, and fix itself to bodies in the 
manner of an Actinea. ARisitoTLE states in several places in his History of Ani- 
mal, that the Actinea (axa#npn) can detach itself from the rock and swim. Thus,” 
in Book iv. 6, speaking of these animals, he writes,—* moomeDuKE fey yg THIS TETPOUS 
domneg tua rav doreuxodeguav, dmorvercs & evore.’ Commentators have supposed that he 
confounded Actineze with Medusee. But he mentions the latter animals under 
another name. The discovery of the Avachnactis, and its abundance in the 
Grecian seas explain the difficulty, and shew the accuracy of his observations. 
Plancia. New Genus.—Umbrella hemispherical ; radiating vessels four, 

