inhabiting the Estuary of the Dee. 199 
the grotesque bowing forms of Caprella Phasma and C. linearis. 
In addition to this host of animals, the rocks are occupied with 
an abundance of boring Mollusks, particularly Pholas crispata, 
with here and there specimens of Sazicava arctica; and their 
slippery surfaces afford to the special searcher several Tunicates, 
such as Ascidia, Clavellina, and Botryllus ; while Tapes pullastra, 
Chiton cinereus, Trochus cinerarius, Purpura, and Buecinum are 
among the shelled Mollusks, as well as occasionally some less 
common. Even fish are sometimes entangled in the pools, and 
may be taken by the hand, such, for instance, as the Spotted 
Gunnell (Murenoides guttata), and the Three-bearded Rockling 
(Motella vulgaris) frequently, and occasionally the Father Lasher 
(Cottus bubalis), the Black Goby (Gobdius niger), the Fifteen- 
spined Stickleback (Gasterosteus spinachia), and the Power Cod 
(Morrhua minuta). 
Such is the hunting-ground at Hilbre Island; and when it is 
borne in mind that all these and many more, and often rarer, 
animals are found in a space which might be traversed from end 
to end, but for the impeding rocks, in five minutes, it will be 
conceded that it is a singularly rich locality. Moreover, I have 
not yet alluded in this sketch to that tribe which is the especial 
subject of this paper (the Nudibranchiata), of which no less than 
twenty-two species have been found in this contracted spot, some 
of them being of the highest rarity and interest. 
The second known specimen of the exquisite Eolis Landsburgii 
was taken by my friend Mr. Byerley at Hilbre Island in 1849. 
In August 1859 I met with a specimen at the same spot, having, 
as previously stated, found it in the Mersey in April of the 
same year. 
Tritonia Hombergii is more frequently met with at Hilbre 
Island than in any part of the Mersey; indeed, although con- 
sidered a deep-sea species, the island is seldom visited without 
a specimen being taken. I refer to it particularly here, because 
in August 1859, Mr. Moore the curator of the Liverpool Mu- 
seum, visiting the spot, brought home a pure white specimen, a 
very beautiful and extremely rare variety. Mentioning the cir- 
cumstance to Mr. Alder, he writes, “ We. have got Tritonia Hom- 
bergu nearly colourless, but not pure white; generally a little 
inclined to flesh-colour.” That this was not a mere sickly indi- 
vidual, is proved by the remarkable fact that it, together with 
some specimens of Holts papillosa, which were taken at the same 
time, lived under Mr. Moore’s care for four months. _ It is gene- 
rally difficult to keep the Nudibranchiata alive in confinement for 
more than a week or two, or at most a month; and indeed, if 
placed in an aquarium, the larger species at least usually perish 
in a few days. The secret of the present success lies, I think, 
