On Marine Dredging. 359 



seas. Scalaria Greenland ica, the ordinary habitat of which is sufl^ 

 ciently explained by its specific name, will henceforward take its place 

 among British niollusca, in consequence of my having, in the month 

 of July last, dredged a fragment of it off Duncansby Head, in about 

 35 fathoms, at the distance of 12 miles from land. Two species, 

 Margarita carnea and Crenella elliptica are found at Oban, but not 

 further south. The only other British localities that I am acquainted 

 with for the former, are Zetland and Orkney ; the latter is met with 

 in the northern Hebrides, but has hitherto been esteemed extremely 

 rare. I found it in extraordinary abundance at Unst, the most 

 northern of the Zetland Islands. 



Astarte compressa, A. elliptica, Nucula tenuis, Pecten nebulosus, 

 Patella ancycloides, Cemoria Flemingii, Natica Montagui, Velutina 

 ovata, Chemnitzia rufescens, Cyclostrema Zetlandica, Rissoa abyssi- 

 cola, Fusus barvicencisj Pleurotoma Boothii, Trichotropis borealis, and 

 probably some others, inhabit the waters of the Clyde, where their 

 range appears to terminate. Ampidesma intermedia, Crania Norwe- 

 gica, Terebratula caput serpentis, andLottia fulva, are present in the 

 Clyde, from whence their range crosses the north channel and ex- 

 tends by the west of Ireland. Lottia testudinaria, a species of Iceland 

 and the arctic regions, unknown on the east coast of Scotland, and even 

 in Zetland, is abundant through the Hebrides, and reaches to the 

 north coast of the Isle of Man. Fusus Bamffius, a shell of Green- 

 land, is frequent in the neighbourhood of Point Lynas, but I do not 

 believe to be found south of Anglesea. Emarginula crassa, first 

 known as a fossil of Sweden, though a living inhabitant of Scandi- 

 *navia, was discovered a few years ago in the Hebrides and Clyde ; 

 and I have very recently received specimens of it, taken alive with 

 oysters on the coast of Carnarvonshire. 



From what I have stated, it would appear that the two points 

 on the west coast of Britain, where the greatest change takes place 

 in the species and genera of moUusca, are — the parallel of our most 

 southern shores and that of the Clyde. Respecting the east coast I 

 cannot speak from personal observation, my researches having been 

 limited to the most northern shores of it. 



At the time of that important and comparatively recent geologi- 

 cal change, when were elevated into dry land those deposits of what 

 has been called the glacial epoch, which we see largely developed in 

 the Clyde basin, the shores of the Irish Sea, including the north 

 portion of the Isle of Man, and of which we have a nearer example 

 in the river bank at Egremont ; several northern forms of moUusca, 

 previously distributed throughout our seas, became either quite ex- 

 tinct in them, or confined to particular localities, which were probably 

 less affected by the general disturbance. These tracts, where survive 

 — though somewhat degenerated in certain instances — the represen- 

 tatives of a more ancient fauna of our seas, are situated principally 

 among the lochs and islands on the west of Scotland ; but there is 



