226 



GEOLOGICAL SUCCESSION OF ANIMALS. 



which are marine worms, surrounded by a solid sheath. The 

 class of Insects is entirely wanting. 



477. The inferiority of the earliest inhabitants of our 

 earth appears most striking among the Vertebrates. There 

 are as yet neither reptiles, birds, nor mammals. The fishes, 

 as we have said, are the sole representatives of this division 

 of animals. 



478. But the fishes of that early period were not like 

 ours. Some of them had the most extraordinary forms, so 

 that they have been often mistaken for quite different ani- 

 mals ; for example, the Pterichthys, (a,) with its two wing- 



a 



Fig. 157. 



like appendages, and also the Coccosteus (I) of the same 

 deposit, with its large plates covering the head and the ante- 

 rior part of the body. There are also found remains of 

 shark's spines, (e,) as well as palatal bories, (rf,) the latter of a 

 very peculiar kind. Even those fishes which have a more 

 regular shape, as the Dipterus, (c,) have not horny scales 

 like our common fishes, but are protected by a coat of bony 

 plates, covered with enamel, like the gar-pikes of the 

 American rivers. Moreover, they all exhibit certain char- 

 acteristic features, which are very interesting in a physio- 

 logical point of view. They all have a broad head, and a 

 tail terminating in two unequal lobes. What is still more 

 curious, the best preserved specimens show no indications 



