UPPER PALAEOZOIC FAUNAS 167 



of new forms. The most noteworthy advance was the 

 appearance of Tectibranchiate and Pulmonate Euthy- 

 neura. Cephalopods were chiefly responsible for the 

 importance of the Upper Palaeozoic Molluscan fauna. 

 Nautiloids were in an acmaic stage during the Devonian, 

 and remained abundant in the Carboniferous ; while 

 Am monoids arose in the former period and were 

 approaching their transcendent acme in the Permian. 

 It is unfortunate that conditions were unsuitable for 

 successful life or fossilization of Mollusca in the British 

 area except in the Carboniferous. 



Prionodesmacea were still the most important, though 

 not the only, Pelecypoda of the Upper Palaeozoic. 

 Palaeoconcha were better developed in the Carboniferous 

 than at any other period; Sanguinolites and Cardio- 

 morpha are two familiar types. Among Taxodonts 

 Nuculana and Leda are often abundant, especially in 

 the Lower Carboniferous of Scotland ; while Parallelo- 

 don, a form which, with its descendants, was important 

 in Mesozoic and Cainozoic faunas, appeared in the 

 Devonian. Schizodonts were the most prolific Upper 

 Palaeozoic bivalves. Conocardium^ a curious and some- 

 what problematical type, is found in the Carboniferous 

 Limestone. The Pteriidae were abundantly represented. 

 Pteria and P seudomonotis appeared in the Devonian, 

 but both genera are more characteristic of Mesozoic 

 horizons. Posidonomya (PI. xii. fig. i) is an important 

 fossil of the Lower Carboniferous. The Pernidae, 

 destined to rise to great prominence in the Mesozoic, 

 had their origin in the little Bakewellia of the Permian. 

 True Ostreidae occur in the Carboniferous, and Schizodus 

 initiated (in the Permian) the essentially Mesozoic family 

 of the Trigoniidae. One of the most characteristic series 

 of Upper Palaeozoic Schizodonts were the Cardiniidae. 

 Naiadites and Carbonicola occur in swarms in some 



