PENGELLY — ON THE DEYOXTAX AGE OF THE WORLD. 
345 
little distance forward from the body. By such a process, the head 
vv ould be inverted, and in such a way that the severed parts w^ould 
take the relative positions which have been described. 
All the British Devonian Cephalopoda are Tetrabranchiate, and 
every family of the order occurs amongst them. Nautilidoe is repre- 
sented by two genera, Chjmenia and Nautilus. The former contained 
eleven species, all confined, in Devon and Cornwall, to Petherwin. 
The genus appears to have been restricted to Devonian times. 
Ortlioceraiidce also had two genera, Ortlioceras and Cyrtoceras. The 
fii'st contained twelve species, of which one is recorded as occurring 
in continental Europe, and three in carboniferous rocks. It does 
not appear that any have been found in Lower Cornwall or Lower 
Xorth Devon. They differ much in the inclination of the sides, the 
se23tal distances, the situation and character of the siphunculus, and 
the inclination of the septa to the sides of the shell, though it is 
I'ossihle that the obliquity of the septa may have been caused by dis- 
tortion, it is scarcely prohahle, seeing that in different specimens 
from different loc.alities the amount or degree of obHquity appears 
to be constant. In one species the siphunculus is remarkable as 
forming a discontinue qs line in passing from chamber to chamber. 
This genus was richer in species, and many attained a larger size in 
the Silurian and Carboniferous than in the age under consideration. 
Cyrtoceras had thirteen British Devonian species, all of which, ex- 
cepting only C. rusticum, probably a synonym for Ortlioceras arcuatum, 
are in Britain confined to South Devon. Species belonging to this 
genus occur before and after, but it attained its maximum specific 
development in, the Devonian age. The family Ammonitidce was 
represented by the single genus Goniatites, the first bom of the family, 
and which dates its advent in this period, when, in the British isles, 
it numbered ten species, all of which are met with in Devon and 
Cornwall : one of them occurs in continental Europe, and three 
passed upwards into Carboniferous times, when the genus attained 
its maximum development ; it outlived the Palaeozoic epoch, and 
finally disappeared in the Triassic period. 
Want of time has rendered it necessary to pass over the other 
classes of mollusca, as well as the entire flora of the period ; and 
from the same cause attention has been mainly given to the Devo- 
nian beds of the South of Britain. 
Though, with the exception of a scale of Holojptyclinis, found, 
according to Professor Phillips, at Meadfoot, near Torquay, and ano- 
ther at Baggy point, in North Devon, ichthyolites are not recorded 
as occurring in the Devonian rocks of Devon and Cornwall, it is 
nevertheless certain that fish did exist within the area during the 
period under consideration ; as a fossil found a few years since in 
the Sterjanodictyuni beds near Looe, in Cornwall, has been pronounced 
by Sir Philip Egerton and other eminent palaeontologists to be an 
ichthyodorulite, or defence-spine of a fish ; and it is probable that 
other, though less well marked, specimens have been met with in 
the same district. 
VOL. IV. 2 N 
