134 



THE MIDDLE PAST. 



pattern, but still preserving that similarity of design which 

 has ever characterised their beautiful structures. The deep- 

 sea, infusorial-feeding brachiopods, though specifically fewer 

 than in the palaeozoic periods, are still abundantly repre- 

 sented terebratula, rhynchonella, spirifera, discina, and 

 the like, being the dominant forms in the marine beds of 



1, Spirifer ; 2, Avicula ; 3, Terebratula ; 4, Pholadomya ; 5, Modiola ; 6, Gryphaea ; 

 7, Trigonia ; 8, Plagiostoma ; 9, Pleurotomaria. 



the lias and oolite. The true bivalves, now so greatly in 

 the ascendant, present themselves in vast profusion, throng- 



