24 Dr M. Sars on Shells from the Earlier and 
7. Suphonodentalium vitreum, Sars.—Only found in Fin- 
mark, north coast of Norway; rare; fossil pretty frequent 
in the oldest beds. This fact, and its present rarity, seem 
to indicate that it is dying out. 
8. Pecten islandicus, Mull.—Distinctively Arctic ; found 
on north coast of Norway and Russia, Greenland and east 
coast of America; goes south as far as the Christiania fjord 
and Bohuslin, but does not reach Britain; diminishes in 
frequency and size as it comes south ; fossil frequent, agrees 
in size with the northern specimens. 
9. Lima excavata (ostreea), J. C. Fabr.—A large species, 
well known on our west coast, and probably to be reckoned 
as Arctic, though found to the south as far as Bohuslan ; it 
lives only in the region of the deep-sea corals, at from 150 
to 300 fathoms ; fossil, in the lowest clay, also found amongst 
the innumerable dead masses of Oculina prolifera (which 
see, p. 25), at a depth below the sea of from 10 to 15 - 
fathoms on the Drébak bank, which must therefore have 
been elevated at least 185 fathoms, or 800 feet. 
10. Arca raridentata, Wood. Pectunculoides, Scacchi. 
——Common along our whole coast; extends south to Gib- 
raltar and even to the Aigean Sea, but in the far north 
attains a much larger size than to the south, and may there- 
fore be considered as arctic ; varies very much in form, both 
in length and depth, and in the projection of its umbo. The 
hinge teeth increase in number with age. It is both in its 
living and fossil state covered with a hairy membrane, 
though Forbes and Hanley state the contrary. Fossil, it is 
very frequent in the lowest clay, where the shells are found 
in pairs. It is so much larger than, and different from, the 
living specimeus, as at first to appear specifically distinct, 
but the transitions between the two prove their identity. 
The great projection backwards of the ventral margin, and 
the great number of cardinal teeth—two respects in which 
the difference between the fossil and the living form is most 
marked—appear to be merely the effects of age and growth. 
It is a curious fact, that this species, which extends back 
into the newer Pliocene of Apulia and Sicily, and the 
Coralline Crag of England, appears there in the smaller 
form which it bears in its more southern habitats at the 
