1 76 INVERTEBRATE PALAEONTOLOGY 



new ones is manifest. Tetracoralla, Stromatoporoids, 

 Blastoids, Camerate Crinoids, Perischoechinoids, Crypto- 

 stome and Trepostome Polyzoa, Orthid, Strophomenid, 

 Productid and Spiriferid Brachiopods, many groups of 

 Pelecypods and Gastropods, Orthoceratid and Gonia- 

 titic Cephalopods, Trilobites and Eurypterids, are some 

 of the more important series of Upper Palaeozoic 

 Invertebrates that either failed to survive the Permian, 

 or lingered, reduced to almost negligible proportions, 

 into the Mesozoic. In place of the heavy casualties in 

 Permo-Triassic evolution, appeared the Hexacorals, true 

 Echinoids, Rhynchonellid and Terebratulid Brachiopods, 

 Oysters and Trigonias, Naticas and Pleurotomarias, and, 

 above all, Ammonites and Belemnites. Many of these 

 types had been in existence in the Upper Palaeozoic, 

 but their prominence was postponed until the Trias. 

 In like fashion, most of the types predominant in the 

 Cainozoic had their origin in the Trias (the Mammalia 

 being noteworthy), but were content with a lowly 

 position in Mesozoic faunas. 



(B) PROTOZOA 



Foraminifera are usually abundant, even to a rock- 

 forming degree, in Mesozoic deposits, but Radiolaria are 

 less conspicuous. The former group was sparingly 

 developed in the Trias (absent from British " New Red 

 Sandstones "), but in Jurassic clays and limestones it 

 began to show that diversity and abundance that 

 culminated in the Upper Cretaceous. As regards the 

 quality of the tests, Mesozoic Foraminifera are closely 

 comparable with those of the present day calcareous, 

 multiperforate types predominating over arenaceous 

 forms. The most important series of the latter type is 

 that of the Lituolidae; some members of the family 



