72 EVOLUTION IN THE PAST 



CORALS Many old forms of corals had passed away ; or, if they 

 can be said to have survived, it was only in modified 

 descendants. One family {Poritidce), which came in view in 

 sparse numbers in the Carboniferous Period, was now 

 markedly in the ascendant. The success of these corals was 

 probably due to their possessing perforated body-walls, and 

 their enjoying, therefore, a greater community of life. At the 

 present day their descendants are in great evidence on the 

 Australian barrier-reef. 



Many colonies were also in existence composed of corals 

 in sohd body-walls : and descendants of some of these less 

 sociahstic communities are still living (Stephanocoenia). 



SEA-LILIES Crinoids, or " sea-hUes," were slowly recovering from 

 Permian afflictions ; but their convalescence was no prelude 

 to a renewal of whilom vigour. They were certainly more 

 modern in structure. This may be gathered from the manner 

 in which the " arms " were attached to the cup ; and from 

 the fact that the exposed mouth — rare in earher times — had 

 become general (Encrinidce, Pentacrinidce). 

 SEA-URCHINS The lead in " spiny-skinned " Ufe was in this Period 

 being taken by sea-urchins. With most of these the body- 

 covering had been consohdated into twenty vertical rows of 

 plates — the regulation number at the present day. A few 

 reactionary forms with more than twenty plate-rows appeared 

 occasionally in later times ; but sea-urchins in tests of that 

 character practically made their last appearance in this 

 Period. 



POLYZOAKS Among Polyzoans, the colonies with zooids in open- 

 mouthed tubes had entirely eclipsed those in which the 

 zooid-tubes were " hidden-mouthed." Indeed there is little 

 or no evidence that the latter colonies were even in existence. 

 There is, however, reason to think that they were undergoing 

 important improvements, the installation of which was 

 involving them in temporary difficulties. 

 LAMPSHELLS Brachiopods were stiU on the downward path. More 

 families had become fossil : but some of long standing and 

 noted for weU-beaked shells, were exhibiting no little vigour 

 (Rhynchonellidce, Terebratulidce). 



Bivalved molluscs retained, in great part, a mixed and 



