94 THE STORY OF THE EARTH. 



coniferous period. Some layers are character- 

 ized by a few peculiar genera, Mich as the conti- 

 nental deposits in the Middle Devonian known 

 from the Brachiopod Stringoccphalus, as Stringo- 

 cephalus limestone; and from the coral Calceola 

 as Calceola slate, which give a distinctive char- 

 to the Devonian period. It is in the 

 Devonian age that we are particularly impressed 

 with the abundance on the earth of types of life 

 which enter largely into the existing fauna. 



Fishes have hitherto been few in number, but 

 some of those remarkable fishes Pterichthys which 

 occurred at the top of the Ludlow beds, together 

 with Coccosteus and the great scaled fringe-finned 

 HoloptychiuSy are found in the marine Devonian 

 beds <>t the continent, as well as in the old red 

 sandstone of Scotland. 



In this period commence several marine uni- 

 valve shells such as Natica y Nerita^ Trochus y 

 vAvs, which are so important in the sea-shore 



i >f the present day. 



They are associated with two very interesting 



halopods. Nautilus i occurs acc< impanied by 

 the remarkable Nautiloid shell named Cfymem'a, 



which has a fold m each septum which divides 

 chamber from another, similar to the fold 



which i> observed in the septa of many tertiary 

 of Nautilus, which are similarly corn- 

 to side. Those compn - 



i have the little tube named the 



siphuncle which p&sses through the septa pla 



in a more inward position than is usual in Nau- 

 tilus. 'Plus genus Clymenia has the siphuncle as 



IS to be m contact 



with th( - d coil. The genus is 



ntrast to aflother remarka- 



