Ch. XXVI.] 



TERM " DEVONIAN." 



419 



PtericMJiys, Agassiz; upper side, showing 

 mouth', as restored by H. Miller.* 



Five species of Ptericlithys have been found in this lowest divi- 

 sion of the Old Eed. The wing- 

 '"■ ■ like appendages, whence the 



genus is named, were first sup- 

 posed by Mr. Miller to be pad- 

 dles, like those of the turtle ; but 

 Agassiz regards them as weapons 

 of defence, like the occipital 

 spines of the River Bull-head 

 (Cottus gobio, Linn.) ; and con- 

 siders the tail to have been the 

 only organ of motion. The ge- 

 nera Dipterus and Diplopterus 

 are so named, because their two 

 dorsal fins are so placed as to 

 front the anal and ventral fins, 

 so as to appear like two pair of 

 wings. They have bony enamelled scales. 



The Asterolepis was a ganoid fish of gigantic dimensions. A. Asmusii, 

 Eichwald, the species characteristic of the Old Red Sandstone of Russia 

 as well as that of Scotland, attained the length of between 20 and 30 

 feet. It was clothed with strong bony armor, embossed with star-like 

 tubercles, but it had only a cartilaginous skeleton. The mouth was 

 furnished with two rows of teeth, the outer ones small and fish-hke, the 

 inner larger and with a reptilian character.f The Asterolepis occurs also 

 in the Devonian rocks of North Ameiica, in the lower division of the 

 Old Red. Coniferous wood, with structure showing medullary rays, has 

 likewise been detected in the lower division by Hugh Miller, J who has 

 pointedly dwelt on the importance of the fact, as the oldest example yet 

 known of so highly organized a plant occurring in a rock of such antiquity. 

 South Devon and Cornwall, — Te7i7i Devonian. — A great step was 

 made in the classification of the slaty and calciferous strata of South 

 Devon and Cornwall in 1837, when a large portion of the beds, pre- 

 viously referred to the " transition" or Silurian series, were found to be- 

 long in reality to the period of the Old Red Sandstone. For this reform 

 we are indebted to the labors of Professor Sedgwick and SirR. Murchison, 

 assisted by a suggestion of Mr. Lonsdale, who, in 1837, after examining 

 the South Devonshire fossils, perceived that some of them agreed with 

 those of the Carboniferous group, others with those of the Silurian, while 

 many could not be assigned to either system, the whole taken together 

 exhibiting a pecuhar and intermediate character. But these paleonto- 

 logical observations alone would not have enabled us to assign, with accu- 



* Old Red Sandstone. Plate 1, fig. 1. Mr. Miller's description of the fish is 

 most graphic and correct. 



I Footprints of the Creator, by Hugh Miller, 

 .■j: Footprints, p. 199. 



