DEVONIAN PERIOD 45 



were now represented by various old and new forms. The 

 colonies with open-mouthed zooids still seemed to be keeping 

 ahead (Cyclostomata) ; and one family, which had first 

 appeared in the preceding Period, and was notable for the 

 large size of its zooids, became exceedingly prosperous 

 (Fistuliporida). Among the " hidden-mouthed " the later 

 developed colonies several new families were becoming estab- 

 lished ; but an old family of Ordovician date, whose members 

 resembled the " lace coral " of our own times, was dominant 

 in this division (Fenestellida). 



Lampshells were now declining ; but they were by no means LAMPSHELLS 

 descending rapidly from their zenith. Those in old-fashioned 

 shells, without hinges, were certainly facing the turn of events 

 with ever-weakening forces ; and some old families had 

 become fossil. But some forms of later development in hinged 

 shells well maintained their position. Those, for instance, 

 in shells of butterfly outline, were now in great force, and 

 widely distributed (Spirifer*), And the pressure of conditions 

 was elsewhere eliciting responses, resulting in important 

 modifications. Some brachiopods, for instance, now had their 

 " arms " gathered up within the shell in simple loops. This 

 new fashion, it may be supposed, brought some advantages 

 relating to breathing and feeding ; for its followers made 

 great progress, and atoned in part for reverses incurred by 

 brachiopods in other divisions of the Order (Terebratella). 



Sea-urchins were no longer to be seen in such primitive SEA-URCHINS 

 tests as protected many of the Silurian forms. All the animals 

 were now in fairly strong body-coverings, and possessed, 

 moreover, well-developed jaws. The descendants of the 

 rigidly encased Silurian animals probably held the lead 

 (Palczechinus}. In other forms the tests were made up of 

 stout plates, but, as these overlapped, the old feature of 

 flexibility no longer urgent was still retained (Lepido- 

 centrus). All the tests still notably differed from those of 

 existing urchins, owing to an excessive number of vertical 

 plate-rows. Modifications, however, were in progress in the 

 direction of economy, and also of greater efficiency. 



Brittle-stars were giving distinct signs of progress. In BRITTLE- 

 addition to those with extremely flexible arms, some forms STARS 



