198 Dr. C. Collingwood on the Nudibranchiate Mollusca 
for about a mile and a half, and rising at intervals into three 
small islands, called respectively Hilbre, Middle Island, and 
Little Eye. Hilbre is the largest and most seaward of these ; 
nevertheless at low water three sides of it are left uncovered by 
the tide, and it is only a portion of the north-western side which 
is sufficiently steep and rocky to harbour marine animals. The 
other two islands are left high and dry at low water. Two miles 
higher up the river are some rocky prominences named Caldy 
Blacks, which are seldom visited, partly from their distance, and 
partly because the tide rushes up the Dawpool Deeps so rapidly 
and so insidiously, that, without great caution and some expe- 
rience, the visit is not unattended with danger. Still it is 
necessary that these rocks should be mentioned, because at least 
one Nudibranch of rarity and interest has been obtained there. 
It is the north-west corner of Hilbre Island, however, which is 
the el Dorado of Liverpool marine zoologists ; and it is really, for 
its extent, a spot of singular richness, but at the same time 
sufficiently difficult of access to render a visit to it an event of 
interest and importance. The low-water mark is fringed with a 
conspicuous belt of Alcyonium digitatum, interspersed with nu- 
merous specimens of Sagartia sphyrodeta (Gosse) and Actinoloba 
dianthus, with here and there an individual of Sagartia viduata ; 
while immense and beautifully coloured S. crassicornes are clus- 
tered in masses higher up the rock, together with the ever- 
varying tints of the little S. troglodytes. Elsewhere the rocks are 
encrusted with sponges, such as Halichondria panicea and H. ocu- 
lata ; and in the little rock-pools are abundance of Polyzoa and 
Zoophytes, such as the delicate Crista eburnea and the screw-like 
Bugula avicularia among the former, and Laomedea gelatinosa, 
Sertularia, Campanularia, and Plumularia &c. among the latter, 
mingled with the flower-like clusters of Tubularia indivisa. Be- 
neath nearly every stone may be found numbers of brittle-stars 
(Ophiocoma rosula and O. texturata), which harbour there with 
the two species of Porcelain Crabs, Porcellana platycheles and 
P. longicornis, particularly the latter, and various species of 
Terebella, Nereis, and Phyllodoce. In other spots are thickly- 
planted colonies of the beautiful Fan-Amphitrite (A. ventila-_ 
brum), whose variegated and spiral gills often measure as much 
as 24 inches across. Besides the Crustacea just referred to, 
there are always to be met with Stenorhynchus phalangium, Hyas 
araneus, Cancer pagurus, Portunus depurator, abundance of Her- 
mits (Pagurus Bernhardus and other species) inhabiting shells 
which vary in size from the largest Buccinum and Fusus to the 
smallest Mangelia, the Alsop Prawn (Pandalus annulicornis), 
and a number of minute Crustaceans, such as Nymphon gracile, 
Pycnogonum littorale, Lygia, &e., while every weed is alive with 
