434 



THE PERMIAN PERIOD 



The Brachiopoda are still very abun- 

 dant, especially in the Lower Permian ; 

 they are closely allied to those of the 

 Carboniferous, and, as in that period, 

 the Productids play the most impor- 

 tant role, though many of the species 

 are peculiar to the Permian. 



Mollusca. — In this group very strik- 

 ing changes are to be noted. The 

 Bivalves increase materially in variety, 

 and in addition to ancient genera like 

 Aviculopecten (VII, i) and Myalina 

 (VII, 2) the Permian of India has 

 many new forms, such as Area, Lucina, 

 Lima, etc. The Gastropods require 

 no particular mention, except for the 

 great abundance of the genus Bettero- 

 phon (PL V, Fig. 10). It is among 

 the Cephalopods that the great ad- 

 vance takes place. Orthoceras and 

 Gyroceras continue from the older 

 periods, and many species of the 

 genus Nautilus (VII, 3) are added, 

 but the chief fact consists in the pres- 

 ence of Ammonoids with highly com- 

 plex sutures, far exceeding, in this 

 respect, the Goniatites of the Carbo- 

 niferous, some of which continue to 

 exist alongside of the more advanced 

 farms. The more important new 

 genera of Ammonoids are Medlicot- 

 tia (VII, 4), Ptyc kites, Popanoceras, 

 Waagenoceras, which have been found 

 in Texas, Sicily, Russia, and India. 

 The presence of these remarkable 

 shells gives a strong Mesozoic cast to 

 the Permian fauna. 



