t an area exceeding
in magnitude the utmost limits we can as yet assign to any assemblage of
contemporaneous fossil species. Mr. Cuming obtained more than a hundred
species of shells from the eastern coast of Africa identical with those
collected by himself at the Philippines and in the eastern coral islands
of the Pacific Ocean, a distance equal to that from pole to pole.[917]

Certain species of the genus _Ianthina_ have a very wide range, being
common to seas north and south of the equator. They are all provided
with a beautifully contrived float, which renders them buoyant,
facilitating their dispersion, and enabling them to become active agents
in disseminating other species. Captain King took a specimen of
_Ianthina fragilis_, alive, a little north of the equator, so loaded
with barnacles (_Pentelasmis_) and their ova that the upper part of its
shell was invisible. The "Rock Whelk" (_Purpura lapillus_), a well-known
British univalve, inhabits both the North Atlantic and North Pacific.

_Helix putris_ (_Succinea putris_, Lam.), so common in Europe, where it
reaches from Norway to Italy, is also said to occur in the United States
and in Newfoundland. As this animal inhabits constantly the borders of
pools and streams where there is much moisture, it is not impossible
that different water-fowl have been the agents of spreading some of its
minute eggs, which may have been entangled in their feathers. The
freshwater snail, _Lymneus palustris_, so abundant in English ponds,
ranges uninterruptedly from Europe to Cashmere, and thence to the
eastern parts of Asia. _Helix aspersa_, one of the commonest of our
larger land-shells, is found in St. Helena and other distant countries.
Some conchologists have conjectured that it was accidentally imported
into St. Helena in some ship; for it is an eatable species, and these
animals are capable of retaining life during long voyages, without air
or nourishment.[918]

Perhaps no species has a better claim to be called cosmopolite than one
of our British bivalves, _Saxicava rugosa_. It is spread over all the
north-polar seas, and ranges in one direction through Europe to Senegal,
occurring on both sides of the Atlantic; while in another it finds its
way into the North Pacific, and thence to the Indian Ocean. Nor do its
migrations cease till it reaches the Australian seas.

A British brachiopod, named _Terebratula caput-serpentis_, is common,
according to Professor E. Forbes, to bot