molluscoida: distribution. 299 



provided with spiral arms appeared first, and attained their 

 maximum while the Terebratulidce were still few in number. 

 The subdivision with calcareous spires disappeared with the 

 Liassic period, whereas the genus Rhynchondla still exists. 

 Lastly, the typical group, Terebratulidce, attained its maximum 

 in the Chalk period, and is scarcely yet on the decline." 



