32 POLYXENIA ALDERI. 
seemed greatly at the mercy of the tide, and progressed all one way—shot, as it rolled back- 
ward, forward, or athwart.’ The transparent tumbler gave me this advantage in observing 
it, that I could use a magnifying lens when it approached the side. Notwithstanding this 
advantage, it was some time before I observed the true form of the animal, as Mr. Miller’s 
excellent description had not then been published. The transparent ball that rose above its 
body was so very pellucid, that it was a good while before I observed it all. It rose toa 
considerable height above the buff-coloured body of the animal; and it was elegantly shaped, 
like the fine crystalline shades often placed over stuffed birds, or artificial flowers, or miniature 
figures formed of pure alabaster. The finest crystal vase was clumsiness itself when compared 
with it. It was as fine as the transparent soap-bubble blown out of a pipe; and we doubt 
not that, like this bubble, it would have been iridescent had it been so placed as that the sun 
could have shone on it. Delicate as its fabric was, the vigour of the little creature was very 
remarkable, and has been well compared to the efforts of a strong swimmer, as it alternately 
contracted and expanded its pellucid organization. The margin of its mouth had a close 
fringe of brownish tentacula. By aid of the lens, I could observe that they were drawn in 
when the body was contracted, but that at every stroke they were protruded like forked 
lightning, or like feathered serpents, darting and flashing forth, till they were longer than the 
body of the animal.” (Landsborough, Arran, chapter xvi, p. 260.) 
When I met with this Stomobrachium in 1839, I fortunately made a drawing of it in 
two states, the one (Plate IV, fig. 1, a@ and 6) having much wider reproductive glands than 
the other (Plate IV, fig. 1, ¢), in which they are linear and paler, and reach quite to the 
margin. The former state is identical with that observed by Ehrenberg, who found ova in 
the folds of the ovaries; the latter is not improbably the male animal. 
Genus VI. Potyxenta, Eschscholtz (1839). 
Umbrella spreading, more or less depressed. Ovaries numerous, linear, in the 
centres of triangular spaces which reach nearly to the circumference. Marginal 
tentacles between each pair of ovaries. Peduncle very short, terminating in an oral 
orifice, surrounded by four lanceolate arms. 
Polyxenia Alderi, Forbes. 
Plate IV, Fig. 2 (under the name of P. cyanostilis). 
I have ventured entirely to redefine the genus Polyxenia, and to regard it as represented 
by the beautiful Medusa now figured from a drawing of my accomplished and distinguished 
friend Mr. Alder, who observed it on the coast of Devon, in 1846. The umbrella is expanded, 
and rather depressed, smooth, and transparent. Its margin is deeply notched by sixteen 
indentations, out of which spring as many rosy tentacula, alternately longer and shorter. The 
sub-umbrella is divided into sixteen somewhat triangular spaces, which commence at about 
two thirds of its height, and terminate near the margin. In the centre of each of these spaces 
