my work had hardly been published, when a skilful palaeontologist, M.
Bosquet, sent me a drawing of a perfect specimen of an unmistakable
sessile cirripede, which he had himself extracted from the chalk of
Belgium. And, as if to make the case as striking as possible, this
cirripede was a Chthamalus, a very common, large, and ubiquitous genus,
of which not one species has as yet been found even in any tertiary
stratum. Still more recently, a Pyrgoma, a member of a distinct
subfamily of sessile cirripedes, has been discovered by Mr. Woodward in
the upper chalk; so that we now have abundant evidence of the existence
of this group of animals during the secondary period.

The case most frequently insisted on by palaeontologists of the
apparently sudden appearance of a whole group of species, is that of the
teleostean fishes, low down, according to Agassiz, in the Chalk period.
This group includes the large majority of existing species. But certain
Jurassic and Triassic forms are now commonly admitted to be teleostean;
and even some palaeozoic forms have thus been classed by one high
authority. If the teleosteans had really appeared suddenly in the
northern hemisphere at the commencement of the chalk formation, the
fact would have been highly remarkable; but it would not have formed an
insuperable difficulty, unless it could likewise have been shown that at
the same period the species were suddenly and simultaneously developed
in other quarters of the world. It is almost superfluous to remark
that hardly any fossil-fish are known from south of the equator; and
by running through Pictet's Palaeontology it will be seen that very few
species are known from several formations in Europe. Some few families
of fish now have a confined range; the teleostean fishes might formerly
have had a similarly confined range, and after having been largely
developed in some one sea, have spread widely. Nor have we any right to
suppose that the seas of the world have always been so freely open from
south to north as they are at present. Even at this day, if the Malay
Archipelago were converted into land, the tropical parts of the Indian
Ocean would form a large and perfectly enclosed basin, in which any
great group of marine animals might be multiplied; and here they would
remain confined, until some of the species became adapted to a cooler
climate, and were enabled to double the southern capes of Africa or
Australia, and thus reach other and dis