Chap. IX. GROUPS OF ALLIED SPECIES. 289 



nicnt of a valve can be recorrnizetl ; from all these circum- 

 stances, I infer that, had sessile cirripcdes existed durinn^ the 

 secondary periods, they would certainly have Ijcen preserved and 

 discovered ; and as not one species had then been discovered in 

 oeds of this age, I concluded that this grcjit jrroup had been 

 suddenly develo])ed at the commencement of the tertiary series. 

 This was a sore trouble to me, adding as I thought one more 

 instance of the abrupt appearance of a great group of species. 

 But my work had hardly been published, when a skilful pale- 

 ontologist, M. Bosquet, sent me a drawing of a perfect speci- 

 men of an unmistakable sessile cirripede, Avhich he had him- 

 self extracted from the chalk of Belgium. And, as if to make 

 tlio case as striking as possil)le, this sessile ciiripede was a 

 C'hthamalus, a very common, large, and ubiquitous genus, of 

 which not one specimen has as yet been foimd even in any ter- 

 tiary stratum. Hence we now positively know that sessile 

 cirripedes existed during the secondary period ; and these cir- 

 ripcdes might have been the progenitors of our many tertiary 

 and existhig species. Still more recently Tyrgoma has been 

 discovered by Mr, AA'oodward in the upper chalk. 



The case most frecjucntly insisted on by paleontologists of 

 the apparently sudden appearance of a whole group of species, 

 is that of the teieostean iishes, low down in the Chalk period. 

 This group includes the large majority of existing species. 

 Lately, Prof. Pictet has carried their existence one sub-stage 

 further back ; and some paleontologists believe that certain 

 nmch older fishes, of which the affinities are as yet imperfectly 

 known, are really teieostean. Assuming, however, that the 

 whole of them did appear, as Agassiz maintains, at the com- 

 mencement of the chalk formation, the fact would certainly be 

 highly remarkal)lc ; but I cannot see that it would be an in- 

 superalile objection to these views, unless it could likewise be 

 shown that tlie species of this group appeared suddenly and 

 simultaneously throughout the world at tliis same period. It 

 is almost superfluous to remark that hardly an}' fossil-lish are 

 known from south of the equator; and by running tlu-ougli 

 Pictet's Paleontology it will be seen that very few species are 

 Ivtiown from several formations in Europe. Some few families 

 of (ish now have a confined range ; the teieostean fish miglit 

 formerly have had a simihirly confined range, and after having 

 been largely developed in some one sea, might have spread 

 widely. Nor have we any right to suppose that the seas of 

 the world have always been so freely open from eouth to north 

 13 



