MOLLUSCA 425 



The land life of the Carboniferous seems to be very much more 

 varied and luxuriant than that of the Devonian and it probably 

 was so in reality. It must be remembered, however, that the im- 

 mense development of fresh- water and marshy deposits in the Car- 

 boniferous was much more favourable to the preservation of such 

 fossils than any conditions that the Devonian had to offer. Part, 

 at least, of the striking difference in the terrestrial fossils of the 

 two periods is to be accounted for in this way. 



The Bryozoa become much more important than they had 

 been before, and contribute materially to the formation of the 

 limestones. Characteristic Carboniferous genera are the screw- 

 shaped Archimedes (V, 8), and Chcetetes, while Fenestella con- 

 tinues to be very abundant. 



The Brachiopoda have undergone a marked diminution, as 

 compared with those of the Devonian, though they are still very 

 common. Genera of long standing, like Atrypa and Pentamerus, 

 have died out, but others, like Chonetes (V, 4), Spin/era (V, 5 ; 

 VI, 3), Orthis, and Rhynchonella, are still represented by many 

 species, but most important of all the Carboniferous genera is 

 Productus (V, 3; VI, 4), which has a very large number of 

 species, among them P. giganteus, the largest known brachiopod. 

 The genus Terebratula, which became exceedingly abundant in 

 the Mesozoic periods, has its beginning in the Carboniferous, 

 though we have already found the family represented in the 

 Devonian. 



Mollusca. — The Bivalves are somewhat more abundant than 

 in the earlier periods. Examples of these are Aviculopecten (VI, 8) 

 and Allorisma (VI, 9). Of Gastropods, the same genera that 

 occur in the Silurian and Devonian are continued into the Car- 

 boniferous, such as Bellerophon (V, 10), Euomphalus (VI, 5), 

 Pleurotomaria (VI, 6), Loxonema (VI, 7), Platyceras (V, 9), 

 with the interesting addition of the most ancient land-shells yet 

 discovered. The genus Conula?'ia (V, 12), referred to the Ptero- 

 pods, is common. Among the Nautiloid Cephalopods, Orthoceras 

 still persists, but this group reaches its acme in the number and 

 variety of the coiled shells, many of which represent new genera, 



