THE PERMIAN PERIOD. 199 
feebly represented at the present day, is one which attained its 
maximum development in the Mesozoic period. 
The Univalves (Gasteropeda) are rare, and do not demand 
special notice. It may be ob- 
served, however, that the Palzeo- 
zoic genera Luomphalus, Mur- 
chisonia, Loxonema, and Macre- 
cheilus are still in existence, to- 
gether with the persistent genus 
Pleurotomaria. -Pteropods of the 
old genera Zheca and Conule- 
ria have been discovered ; but 
the first of these characteristi- 
cally Palzeozoic types finally 
dies out here, and the second 
only survives but a short time 
longer. Lastly, a few Cephalopods have been found, still wholly 
referable to the Tetrabranchiate group, and belonging to the old 
genera Orthoceras and Cyrtoceras and the long-lived Wautilus. 
Amongst Vertebrates, we meet in the Permian period not 
only with the remains of Fishes and Amphibians, but also, for 
the first time, with true Reptiles. The /ishes are mainly 
Ganoids, though there are also remains of a few Cestraciont 
Fig. 136.—Av7ca antigua. Permian. 
Fig. 137. —Platysomus gibbosus, a ‘‘heterocercal” Ganoid, from the 
Middle Permian of Russia. 
Sharks. Not only are the Gazoids still the predominant group 
of Fishes, but all the known forms possess the unsymmetrical 
(‘‘heterocercal”) tail which is so characteristic of the Palaeozoic 
Ganoids. Most of the remains of the Permian Fishes have 
been obtained from the “ Marl-slate” of Durham and the 
corresponding ‘‘ Kupfer-schiefer” of Germany, on the horizon 
