26 O.V THE TEMl'uUAL ARCHJiS Ol-' THE ItKPTlLlA. 



l)etter-et|uipped two-arched forms, and we can at present only 

 examine the very specialised aquatic modifications that survived. 

 Jifoovila is probably the only w-ell-known land-form. Arwosceles 

 is probably also a member of the group, but so very early that it 

 still retains the true coracoid. In no other is a true coracoid 

 known. The Mesosaurs are very early aquatic modifications. 

 The Ichtliyosaurs are much later aquatic forms. The Plesiosaurs 

 and Placodonts and Ohelonians are, I believe, all descended from 

 land forms closely similar to Youngina, but with only the upper 

 temporal fossa developed. 



This group of primitive lizard-like forms, which had only the 

 upper temporal fossa developed, and their aquatic descendants 

 the Mesosaurs, the Ichthyosaurs, the Plesiosaurs, and Placodonts, 

 together with the very highly specialised Ohelonians, which I 

 consider to be all related, I proposed to unite in a fourth 

 subclass, which I suggest may be called the Anomapsida. 



