IMPERFECTION OF GEOLOGICAL RECORD 273 



species ; from the extraordinary abundance of the indi- 

 viduals 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 pre- 

 served in the oldest tertiary beds ; from the ease with 

 which even a fragment of a valve can be recognised ; 

 from all these circumstances, 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 instance of the abrupt appear- 

 ance 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 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 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 

 much older fishes, of which the affinities are as yet 

 imperfectly known, are really teleostean. Assuming, 

 however, that the whole of them did appear, as Agassiz 

 believes, at the commencement of the chalk formation, 

 the fact would certainly be highly remarkable ; but 



