Ch. XXY.] 



LOWER CARBONIFEROUS STRATA. 



521 



position 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 palaeontologist, 

 once stated to me that, in making his extensive collection of the fos- 

 sils of the Mountain Limestone of Belgium, he had found no more 

 than four or five examples of the bones or teeth of fishes. Judging 

 from Belgian data, he might have concluded that this class of verte- 

 brata was of extreme rarity in the carboniferous seas; whereas the 

 investigation of other countries has led to quite a different result. 

 Thus, near Clifton, on the Avon, there is a celebrated " bone-bed," 

 almost entirely made up of ichthyolites ; and the same may be said 

 of the " fish-beds " of Armagh, in Ireland. They consist chiefly of 

 the teeth of fishes of the Placoicl order, nearly all of them rolled as 

 if drifted from a distance. Some teeth are sharp and pointed, as in 

 ordinary sharks, of which the genus Cladodus affords an illustration ; 

 but the majority, as in Psammodus and CocJiliodus, are, like the teeth 

 of the Cestracion of Port Jackson (see above, fig. 322, p. 330), mas- 

 sive palatal teeth fitted for grinding. (See figs. 581, 582.) 



Fig. 581. 



Fig. 5S2. 



Psammodus porosus, Agass. Bone-bed, Moun 

 tain Limestone. Bristol ; Armagh. 



CocMiodus contortus, Agass. Bone- 

 bed, Mountain Limestone. Bris- 

 tol; Armagh. 



There are upwards of seventy other species of fossil fish known in 

 the Mountain Limestone of the British Islands. The defensive fin- 

 bones of these creatures are not unfrequent at Armagh and Bristol ; 

 those known as Oracanthus are often of a very large size. Ganoid 

 fish, such as Holovtijchius- also occur ; but these are far less numer- 

 ous. The great Megalichthys Hibberti appears to range from the 

 Upper Coal-measures to the lowest Carboniferous strata. 



Foraminifera. — In the upper part of the Mountain Limestone group 

 m the S. "W. of England, near Bristol, limestones having a distinct 

 oolitic structure alternate with shales. In these rocks the nucleus of 

 every minute spherule is seen, under the microscope, to consist of 

 a small rhizopod or foraminifer. This division of the lower animals, 

 which is represented so fully at later epochs by the JNummulites and 

 their numerous minute allies, appears in the Mountain Limestone to 



