GROUPS OF ALLIED SPECIES. 615 



gigantic size, existed during that period ? Not a fragment 

 of bone has been discovered in these beds. Not long ago, 

 palaeontologists maintained that the whole class of birds 

 came suddenly into existence during the eocene period ; 

 but now we know, on the authority of Professor Owen, that 

 a bird certainly lived during the deposition of the upper 

 green sand ; and still more recently, that strange bird, the 

 Archeopteryx, with a long lizard-like tail, bearing a pair of 

 feathers on each joint, and with its wings furnished with 

 two free claws, has been discovered in the oolitic slates of 

 Solenhofen. Hardly any recent discovery shows more forci- 

 bly than this how little we as yet know of the former inhab- 

 itants 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 num- 

 ber of existing and extinct tertiary species ; from the ex- 

 traordinary abundance of the individuals of many species 

 all over the world, from the arctic regions to the equator, in- 

 habiting various zones of depths, from the upper tidal limits 

 to fifty fathoms ; from the perfect manner in which speci- 

 mens are preserved in the oldest tertiary beds ; from the 

 ease with which even a fragment of a valve can be recog- 

 nized ; 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 de- 

 veloped at the commencement 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 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 sub-family of sessile cirripedes, has been dis- 

 covered 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, 



