92 THE SUCCESSION OF MOLLUSCA. 



many pteropods of larger bulk than those now existing, of 

 the chambered shells of many singular cephalopods (Ortho- 

 ceratites, &c.), and the shells of some gasteropod and bi- 

 valved mollusca. Ascending to the carboniferous formations 

 of this silurian epoch, the molluscan fossils thicken upon us. 

 Brachiopods abound under novel forms ; a larger number of 

 gasteropods and of ordinary bivalves have appeared to aid 

 in the great work ; " but the cephalopodous inhabitants of 

 the seas during the carboniferous period were still the most 

 important and the most numerous of the molluscous ani- 

 mals ; and they included not only the straight shells of Or- 

 thoceratites, but a large number of spirally twisted species, 

 bearing a somewhat different relation to the nautilus. The 

 most important are called Goniatites." * It is from these 

 strata that lime is principally worked ; and in the marble 

 of which your chimney-piece is made, you may trace the 

 figures of shells that have been pictured there by no spor- 

 tive freaks of the formative powers of nature, nor by a 

 spontaneous vegetation, as philosophy once dreamed, but 

 that are the real remains of living creatures which "have put 

 off flesh and blood, and are become immutable." Ascend- 

 ing to the middle epoch, we find, indeed, the former races 

 to have disappeared, but their places are fully occupied by 

 others approximating nigher in character to those of exist- 

 ing seas, " without any of the species being identical, and 

 with little approach even to existing genera." A very large 

 number were among the common tenants of the lias, both 

 brachiopods and bivalved and univalved mollusks ; and an- 

 other large and important group called Ammonites, related 

 to the existing Nautilus. The Belemnite, which was a 

 naked cephalopod allied to the Sepia, was also a common 

 animal, and, with the Ammonites, so thronged some parts 

 of the sea that complete strata seem to have been formed 

 of their remains. In the oolitic seas mollusca swarm even 

 more abundantly : some Terebratulae, in certain localities, 

 lived in beds as oysters now do almost to the exclusion of 

 other animals; the Ammonite was scarcely less abundant 

 than in the preceding period ; and the Belemnite now occurs 

 in the highest perfection, varying in size from specimens 

 not an inch long to others measuring upw r ards of a foot. 

 The succeeding cretaceous period owes not less to its mol- 

 luscan tenants, and their fossils truly indicate their influence. 

 Bivalved and univalved genera thronged the waters ; and the 



* Ansted's Ancient World, 96. In this popular and pleasant volume, 

 the student will find the successive creations of the mollusca carefully indi- 

 cated, and good figures of the most remarkable and characteristic species. 



