THE PERMIAN PERIOD 



191 



Porifers were present though they are not common in fossil 

 form. 



Coelenterates. — An important change took place in the evolu- 

 tion of the Corals because of the first appearance of more modern 

 Hexacoralla, or forms whose septa or dividing walls were six in 

 number or multiples of six. The Paleozoic Tetracoralla, however, 

 still continued to be common. 



Echinoderms. — So far as the records show, this sub-kingdom 

 diminished in an extraordinary manner, though Crinoids, Aster o- 

 zoans, and Echinoids were present. 



Molluscoids. — Bryozoans were 

 abundant. 



Brachiopods continued to be com- 

 mon with straight-hinged types, so 

 abundant through the Paleozoic era, 

 still prevalent for the last time. 



Mollusks. — Pelecypods continued 

 to increase in numbers and species, 

 while Gastropods much like the older 

 Paleozoic forms were still common. 



Cephalopods. — Some early Pale- 

 ozoic types of Nautiloids (e.g. Orthoc- A Permian chambered Cephalc™ 

 eras and Gyroceras) still persisted and vod,Waagenoceras cumminsi 

 y . /,. ^ , (White) showing highly 



various species of the modern genus folded suture (par tition) 



Nautilus were added. The Ammonoids lines. 



show the most interesting evolutionary 



changes, because of the notably increased complexity of their 



partition or suture structures. A good example is shown in Fig. 



115 which is really more suggestive of Mesozoic Ammonites than 



of Paleozoic Nautiloids. 



Arthropods. — Among the Crustaceans and Arachnids the 

 groups of Trilobites and Eurypterids became extinct. In fact they 

 had but few representatives in the Permian. 



Insects have been found in abundance, especially in the 

 Permian of Kansas and, though the species are different, they 

 were much like those of the Pennsylvanian. 



Vertebrates. — Fishes were in general very similar to those of 

 the Mississippian and Pennsylvanian, though there were various 

 species and genera changes. 



Amphibians. — In general it may be said that the Permian 



Fig. 115 



