APPEARANCE OF WHOLE GROUPS 357 



lizard-like tail, bearing a pair of feathers on each joint, and 

 with its wings furnished with two free claws, has been dis- 

 covered in the oolitic slates of Solenhofcn. Hardly any recent 

 discovery shows more forcibly than this, how little we as yet 

 know of the former inhabitants of the world. 



I may give another instance, which, from having passed 

 under my own eyes, has much struck me. In a memoir on 

 Fossil Sessile Cirripedes, I stated that, from the large number 

 of existing and extinct tertiary species ; from the extraordi- 

 nary 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 fragment of a valve can be recognized ; 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 com- 

 mencement of the tertiary series. This was a sore trouble 

 to me, adding as I then thought one more instance 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 un- 

 mistakeable 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 sub- 

 family 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 palccontologists of 

 the apparently sudden appearance of a whole group of species, 

 is that of the teleostean fishes, low down, according to Agas- 

 siz, in the Chalk period. This group includes the large ma- 

 jority of existing species. But certain Jurassic and Triassic 



