214 



OUR COMMON BRITISH FOSSILS, 



hardly doubts that sea-squirts were in existence in 

 the eadier seas of the globe. Had we any fossil 

 evidences of them, they might be serviceable in 

 tracing the original connection between the Inverte- 

 brates and the Vertebrates. 



These sea-mats are also related to another group 

 of animals which, as we have already seen, played a 

 very active part in the seas of the Palaeozoic epoch — 

 the Lamp-shells or Brachiopoda. In fact, sea-mats, 



Fig. ■no.— Q^Ws.oiFlustra 

 (magnified 60). 



Fig. 171.— Social Ascidians {Boirylins), 

 on Sea-weed (natural size).j 



sea- squirts, and lamp-shells are all grouped in the 

 division Molhiscoida. 



It is a common error to associate the sea-mats 

 with the Corallines. In reality these two groups of 

 animals are widely separated by zoological characters, 

 although not unfrequently they greatly resemble each 

 other as far as external characters go. 



The most beautiful, and perhaps also the most 

 extensive, of the ancient sea-mats were the Fenestellidce. 



