436 
ELEMENTS OF GEOLOGY. 
Fij?. 489. 
mg. 488. More than twenty species of the genus 
Bellerophon (see Fig. 488), a shell like the 
living Argonaut without chambers, occur 
in the Mountain Limestone. The genus 
is not met with in strata of later date. 
It is most generally regarded as belong¬ 
ing to the pelagic Nucleobranchiata and 
Bellerophon costatus, Sow. the family Atlantidge, partly allied to the 
Mountain Limestone. • • ili n 
Grlass-feheil, (Jarinaria; but by some lew 
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 or¬ 
der; yet they offer some remarkable forms. 
Among these is Orthoceras^ a siphuncled 
and chambered shell, like a Nautilus un¬ 
coiled and straightened (Fig. 489). Some 
species of this genus are several feet long. 
The Goniatite is another genus, nearly al¬ 
lied to the Ammonite.^ from which it dif¬ 
fers in having the lobes of the septa free 
from lateral denticulations, or crenatures; 
so that the outline of these is angular, con¬ 
tinuous, and uninterrupted. The species 
represented in Fig. 490 is found in most Portion oij)rihoeeras la- 
localities, and presents the zigzag charac¬ 
ter of the septal lobes in perfection. The 
dorsal position of the siphuncle, however, clearly distinguishes 
the Goniatite from the Nauti¬ 
lus, and proves it to have be¬ 
longed to the family of the 
Ammonites, from which, in¬ 
deed, some authors do not be¬ 
lieve it to be generically dis¬ 
tinct. 
Fossil Fish. — The distribu¬ 
tion of these is singularly par- 
Goniatites crenistra.'PhiWms. Mountain crk fLnf M rlo 
Limestone. North America, Britain, mucil SO, Wiat IVl. Oe 
Germany, etc. Koninck of Liege, the eminent 
a. Lateral view. 6. Front view, showing palaeontologist, once Stated tO 
the mouth. that, in making his exten¬ 
sive collection of the fossils 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 vertebrata was 
of extreme rarity in the carboniferous seas; whereas the in- 
terale. Phill. Mount¬ 
ain Limestone. 
Fig. 490. 
