PENGELLY — OX THE DEVONIAN AGE OF THE WORLD. 



345 



little distance forward from the body. By such a process, the head 

 would be inverted, and in such a way that the severed parts would 

 take the relative positions which have been described. 



All the British Devonian Cephalopoda are Tetrabranchiate, and 

 every family of the order occurs amongst them. Nautilidce is repre- 

 sented by two genera, Clymenia imaNautilus. The former contained 

 eleven species, all confined, in Devon and Cornwall, to Petherwin. 

 The genus appears to have been restricted to Devonian times. 

 Ortkoceratidce also had two genera, Orthoceras and Cyrtoceras. The 

 first 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 

 North Devon. They differ much in the inclination of the sides, the 

 septal distances, the situation and character of the siphunculus, and 

 the inclination of the septa to the sides of the shell, though it is 

 possible that the obliquity of the septa may have been caused by dis- 

 tortion, it is scarcely probable, seeing that in different specimens 

 from different localities the amount or degree of obliquity appears 

 to be constant. In one species the siphunculus is remarkable as 

 forming a discontinuous 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 G. rusticum, probably a synonym for Orthoceras 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 born 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 Soloptycliius, 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 Steganodictyum 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 



