THE AGE OF INVERTEBRATES OF THE SEA. V 



dawn of the Tertiary ; yet the genus Nautilus, one of the oldest 

 and least improved of the whole, survived, and still testifies to 

 the wonderful contrivance embodied in these animals. 



These are merely general considerations, but Barrande, in his 

 Etudes Generales, goes much farther. He sums up all the known 

 facts in the most elaborate manner, considering first the em- 

 bryonic characters of the shell in the different genera, then their 





Fig. 73. — Cretaceous Ammonltidae, 

 a, Baculites. b, Ancyloceras, c, Crioceras. d, Turrilites. 



distribution in space and time, then all the different parts and 

 characters of the shells in the different groups — the whole with 

 reference to any possible derivation of the species ; and he 

 finds that all leads to the result that in every respect these 

 shells seem to have been so introduced as to make any theory 

 of evolution with respect to them altogether untenable. In his 

 concluding sentence this greatest of Palaeozoic palaeontologists 



