FOSSIL INVERTEBRATED ANIMALS. 479 



fossils which they contain are very similar to the bodies with 

 which we are acquainted in a Hving state in collections of 

 fresh water. This leads us to the presumption that they have 

 existed in a fluid of the same nature. 



It has been said, and frequently repeated, that the majority 

 of the fossils have their living analogues, but that they are 

 either in the deepest abysses of the ocean, or in very remote 

 seas. But the strictest and most extensive observation esta- 

 blishes a multitude of differences between the fossil bodies and 

 those which have been regarded as their living analogues. 



We shall now proceed to the notice of a few of the principal 

 families and genera to which invertebrated fossil remains 

 belong. We must content ourselves with very brief observa- 

 tions on this part of our subject ; for to treat it at large, or enter 

 at all into specific details, would occupy a space totally incon- 

 sistent with our limits. There are many admirable works, 

 which those who are disposed to study this subject minutely 

 may have recourse to with the greatest advantage. Among 

 them, for the fossils of our own island, the Messrs. Sowerby's 

 work on '' Mineral Conchology" stands pre-eminent. 



The Ammonites are a genus of shells of the class of univalves, 

 the characters of which are a discoid spiral^ with contiguous 

 turbinations all apparent, and the internal parietes articulated 

 by sinuous sutures ; they have also transverse partitions, lobated 

 through their centre, and pierced by a marginal tube. 



The fossil shells, which compose this genus, derive their name 

 from their resemblance to rams' horns, the symbol of Jupiter 

 Ammon. They are the cornua Ammonis of oryctologists. 

 They exhibit very great relations with the nautili; but they 

 differ from them essentially by having all the turbinations of 

 their spires visible, while in the nautili they are concealed in 

 the last one. They also differ by having their partitions always 

 more sinuous, and their tube or siphon always placed under 

 the keel of the back. 



The ammonites are regarded as pelagian shells, that is, as 



