408 



FOSSILS OF MOUNTAIN" LIMESTONE. 



[Ch. XXV. 



later date. It is most generally regarded as belonging to the ITeteropoda, 

 and allied to the Glass-Shell, Carinaria ; but by some few it is thought 

 to be a simple form of Cephalopod. 



The carboniferous Cephalopoda do not depart so widely from the living 

 type (the Nautilus), as do the more ancient Silurian representatives of 

 the same order ; yet they offer some remarkable forms scarcely known in 

 strata newer than the coal. Among these is Orthoceras, a siphuncled 

 and chambered shell, like a Nautilus uncoiled and straightened (fig. 529). 

 Some species of this genus are several feet long. The Goniatite is another 



Fig. 529. 



Portion of Orthoceras laterale, Phillips. Mountain Limestone. 



genus, nearly allied to the Ammonite, from which it differs in having the 

 lobes of the septa free from lateral denticulations, or crenatures ; so that 

 the outline of these is continuous and uninterrupted. 



The species represented in fig. 530 is found in almost all localities, and 

 presents the zigzag character of the septal lobes in perfection. 



In another species (fig. 531), the septa are but slightly waved, and so 

 approach nearer to the form of those of the Nautilus. The dorsal position 



Fig. 530. 



Fig. 581. 



GoniatiUs erenistria, Phill. Mountain 

 Limestone. N. America ; Britain ; 

 Germany, &e. 



a. Lateral view. 



&. Front view, showing the mouth. 



Goniatites evolutus, Phillips. 



Mountain Limestone. 



Yorkshire. 



of the siphuncle, however, clearly distinguishes the Goniatite from the 

 Nautilus, and proves it to have belonged to the family of the Ammonites, 

 from which, indeed, some authors do not believe it to be generically distinct. 

 Fossil fish. — The distribution of these is singularly partial ; so much 

 so, that M. de Koninck of Liege, the eminent paleontologist, once stated 

 to me that, in making his extensive collection of the fossils of the Moun- 

 tain Limestone of Belgium, he had found no more than four or five ex- 

 amples of the bones or teeth of fishes. Judging from Belgian data, he 

 might have concluded that this class of vertebrata was of extreme rarity 

 in the carboniferous seas ; whereas the investigation of other coun- 

 tries has led to quite a different result. Thus, near Clifton, on the Avon, 



