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 ujDon 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 moUusks ; 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 upwards of a foot. — 

 The succeeding cretaceovis 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. 



