22 FOSSIL REPTILES OF DORSET. 



neck of the Crocodile ; the sacrum consists of only two vertebrae. 

 The large orbits have no scleroid plates, with the exception of 

 Pies, dolichodeirus. In consequence of the large size of the pre- 

 maxillary bone the nasal aperture is placed far back, and is a little 

 in front of the orbits. Coracoid long, parallel with the axis of the 

 trunk ; scapula short, straight and somewhat flattened, forming 

 with the coracoid cavity glenoid which receives the humerus. 

 The habits of Plesiosaurus were probably marine; this may be 

 inferred from the remains with which they were associated. It is 

 probable, however, that some species ascended rivers, having been 

 found in the Wealden freshwater deposits. The comparatively short 

 tail and large paddles render it likely that the limbs were the chief 

 means of propulsion ; the long neck would tend to impede its pro- 

 gress through the water, and would adapt it better for swimming 

 on or near the surface. The sharp teeth were well suited for 

 catching and holding the fish which formed part of, if not altogether, 

 its food. Plesiosaurus is known to have existed from the time of 

 the Lower Lias to the Chalk. More than fifty British species 

 have been described from different localities. This genus has a 

 wide geographical distribution ; it has been found in Europe, 

 India, Australia, North and South America. 



PLESIOSAURUS DOLICHODEIRUS, Conybeare. 



The head of this species is remarkably small, snout broad and 

 short, temporal fossae broader than long. Neck as long as the body 

 and tail united, and consists of more than forty vertebrae, which 

 articulate by shallow concave surfaces ; the pubis expands into a 

 broad plate, which, with the ischium and the ilium, forms the cavity 

 (acetabulum) to receive the femur. The orbits, as has been already 

 mentioned, are furnished with sclerotic plates ; teeth very slender 

 and curved, about twenty-five in number on each side of the jaws. 

 Found in the Ammonites planorbis zone, Lower Lias, Lyme Regis 

 and Charmouth. 



PLESIOSAURUS ROSTRATUS, Owen. 



Named and described by Sir K. Owen from a perfect skeleton, 

 from the Ammonites Bucklandi zone, Lower Lias of Charmouth. 



