420 



THE GENERAL PRINCIPLES OF ZOOLOGY 



V:; 



representatives of the Elasmobranchii and of a group now 



extinct, the Ostracodermi (Gr. oarpaicov, 

 shell, and Bep/xa, skin) (Fig. 395), which 

 had a well-developed skeleton on the out- 

 side of the body, but as far as we know no 

 hard internal skeleton. The Ganoidei also 

 appeared at this time. Thus this period 

 introduced the vertebrates, but only through 

 some of their more lowly organized repre- 

 sentatives, while it contains no trace of any 

 of the higher classes. 



The Devonian period has often been 

 called the age of fishes because of the 

 W abundance of their remains. The Ostra- 

 codermi and Ganoidei are numerous, and 

 the Dipnoi first appear here ; but there 

 are no Teleostei until we reach a much 

 later period. The Ganoidei attain their 

 maximum development at this time ; they 

 have very few living representatives to-day. 

 The most notable characteristic of all these 

 fishes is the well-developed external skele- 

 ton, consisting largely of a veritable armor 

 4 of very hard scales. 



In the Carboniferous period, which is 

 of great popular interest through its vast 

 forests which gave rise to our deposits of 

 coal, we find appearing, in addition to the 

 animals of the preceding formations, 

 Araneida, Myriapoda, and Insecta; here 

 are found also the first remains of Amphibia 

 belonging to an order now extinct, the Sti 

 cephali (Gr. areya), to cover, and Ke^aX/j, 

 head). Thev usually possessed two pairs of 



Fig. 397. Ceratodus forsteri, , . . -it i 



much reduced. (After Gun- lateral appendages, a tail, and an external 

 the.-, from Parker and Has- skeleton, a structure found in no living 



well's Manual.) . 



Amphibia ; thev were often of great size. 



In the Permian, the last of the Palaeozoic formations, are 



found the first remains of the Reptilia. There is a genus 



