CHAP. IX. ] THE DEEP-SEA FAUNA. 461 
Arctic expedition, which reached 2,600 fathoms, 
when a Cuma and a fragment of an Astarfe, came up 
in the ‘ Bulldog’ machine. He adds, ‘‘ It is evident 
that the majority, if not the whole of our submarine 
(as contradistinguished from littoral or phytopha- 
gous), mollusea originated in the North, whence they 
have in the course of time been transported south- 
wards by the great Arctic currents. Many of them 
appear to have found their way into the Mediterra- 
nean, or to have left their remains in the tertiary or 
quaternary formations of the south of Italy; some 
have even migrated into the Gulf of Mexico.” 
I have great hesitation in questioning any of the 
conclusions of my friend Mr. Gwyn Jeffreys on a 
subject in which he is so excellent an authority, 
but I confess I do not quite see the cogency of his 
reasoning on this point. It would seem rather that 
the last change in the molluscan fauna of the British 
area, at moderate depths, consisted in the retirement 
of northern species at the close of the glacial period 
and the immigration of southern forms. The qua- 
ternary beds of the Clyde district contain a rich 
assemblage of mollusca; those of the neighbourhood 
of Rothesay especially representing the deeper part 
of the Laminarian and the Coralline zone. The 
broad characteristic of the fauna of this bed is 
that many of the most numerous species—for 
example, Pecten islandicus, Tellina calearea, aud 
Natica clauwsa—are now extinct in the seas of 
Britain, but are still met with in abundance in the 
seas of Scandinavia and Labrador ; while many forms 
now extremely common in the British seas and 
having a southern extension are entirely absent. 
