Chap. IX. 
GEOLOGICAL KECOKD. 
305 
number of existing and extinct tertiary species; from 
the extraordinary abundance of the individuals of many 
species all over the world, from the Arctic regions to 
the equator, inhabiting various zones of depths from 
the upper tidal limits to 50 fathoms; from the perfect 
manner in which specimens are preserved in the oldest 
tertiary beds; from the ease with which even a frag¬ 
ment of a valve can be recognised; from all these cir¬ 
cumstances, I inferred that had sessile cirripedes existed 
during the secondary periods, they would certainly have 
been preserved and discovered; and as not one species 
had then been discovered in beds of this age, I concluded 
that this great group had been suddenly developed at 
the commencement of the tertiary series. This was a 
sore trouble to me, adding as I thought one more in¬ 
stance of the abrupt appearance of a great group of 
species. But my work had hardly been published, when 
a skilful palaeontologist, M. Bosquet, sent me a drawing 
of a perfect specimen of an unmistakeable sessile cirri- 
pede, which he had himself extracted from the chalk 
of Belgium. And, as if to make the case as striking as 
possible, this sessile cirripede was a Chthamalus, a very 
common, large, and ubiquitous genus, of which not one 
specimen has as yet been found even in any tertiary 
stratum. Hence we now positively know that sessile 
cirripedes existed during the secondary period; and 
these cirripedes might have been the progenitors of 
our many tertiary and existing species. 
The case most frequently insisted on by palaeontolo¬ 
gists of the apparently sudden appearance of a whole 
group of species, is that of the teleostean fishes, low 
down in the Chalk period. This group includes the 
large majority of existing species. Lately, Professor 
Pictet has carried their existence one sub-stage further 
back; and some palaeontologists believe that certain 
