ON THE SHETLAND CRUSTACEA, TUNICATA, ETC. 249 
have been found in the Moray Firth, but are wholly unknown on the eastern 
coast of England. Moreover, many species have been recorded on the Nor- 
Wegian coast, though never found on the eastern shores of England, and 
therefore may be presumed to have migrated thither up the western side of 
Great Britain and round the north of Scotland; as examples of such species 
may be cited Pleurotoma striolata, attenuata, and septangularis, Cerithiopsis 
tubercularis, Cerithiwm reticulatum and perversum, Rissoa violacea, Pholas 
dactylus, Solen vagina, Psammobia costulata, Gastrana fragilis, Isocardia cor, 
Cardium aculeatum, Lepton squamosum, Xantho rivulosus, Portunus arcuatus, 
Gebia deltura, &e. On the other hand, while northern forms do not extend 
southward on the east coast beyond Yorkshire and the Dogger Bank, on the 
western coasts they in many instances have a range southwards to the 
Nymph Bank, off Cork, and even to the Mediterranean sea. Inasmuch, 
therefore, as migration northwards has for the most part taken place by way 
of the Hebrides and Shetland, a southern form which may be found in 
the Gulf of Christiania or neighbouring part of Scandinavia, though at a point 
of latitude considerably further to the south than Shetland, may be regarded 
practically with respect to distribution to be further north, and a northern 
species at Shetland as further south in its course of migration. In the pre- 
paration, therefore, of the Tables IV. and VII. I have regarded the whole of 
the Scandinavian sea as though it was to the north of Shetland, notwith- 
standing that the latter is geographically situated in about the same latitude 
as Bergen. 
As has been already stated, the chief aim of the Dredging Committee was 
to thoroughly examine the invertebrata of the deep sea. This purpose was 
never lost sight of, and the dredge was rarely let down in the Voes or other 
shallow water except when we were driven there by stress of weather ; nor 
was it possible to find much leisure, amid the constant labour entailed by the 
examination and preparation of the animals procured by the dredge, to devote 
to the littoral zone. Notwithstanding, therefore, the great length of the pre- 
sent catalogue (which shows the fauna in almost every branch to be more 
rich than that of any other portion of the British coast which has been care- 
fully examined by competent naturalists) there cannot be a question that 
numerous and interesting discoveries will reward the future investigations of 
zoologists near the shore as well as in the open sea. For with regard to the 
latter, our repeated dredgings in these northern waters have only sent us 
home each time more fully convinced how much remains to be done before 
we can attain anything like a complete knowledge of the animals which 
inhabit them. We never tried a new locality a few miles distant from that 
which we were before examining that we did not meet with species which 
had been previously unnoticed: in fact the Shetland seas appear to afford an 
inexhaustible treasury of rare animals in every department of zoology. 
While some species are extremely widely diffused, though numerically 
scarce, throughout the province, others are common everywhere, and others 
again apparently excessively limited in their distribution as well as very rare 
when found. But one of the most remarkable features in the distribution of 
life in the Shetland Sea is the extraordinarily circumscribed habitat, but at 
the same time the local profusion, of many species. It will not be without 
interest to give a few examples of this. Many Crustacea, as Wika edulis, 
Doryphorus Gordoni, Gastrosaccus sanctus, &c., occurred on one occasion in 
one spot in considerable numbers, but were scarcely ever (if ever) seen again. 
Forty miles east of the Whalsey Skerries Echinus Norvegicus was in such 
extraordinary profusion that the dredge came up again and again literally 
almost filled with it; but though occurring in many other localities, it was, 
1868. T 
