OPHTHALMOSAIJEUS. 



•51 



The description of the humerus is rendered difficult by the circumstance, that all the 

 specimens in the collection are free and not in their natural position in relation to the 

 rest of the skeleton, as they usually are in the specimens of the Liassic Ichthyosaurs. 

 Consequently it has not been easy to determine with certainty which is the right and 

 which the left, and therefore also which is the dorsal and which the ventral (palmar) 

 face. A further difficulty is also introduced by the fact that when these animals died 

 the paddles seem sometimes to have fallen over on to their dorsal surface, even when 

 the remainder of the skeleton clearly rested on its ventral face. The position of the 

 paddles in several specimens has been carefully noted by Mr. A. N. Leeds, and 

 the following determination of the right and left, and of the upper and lower face, 



Text-fitj. 35. 



Upper surface of restored shoulder-girdle of Oj)hthalmosaurus. (R. 2137, about \ nat. size.) 

 d., clavicle ; cor., coracoid ; i.d., interclavicle ; sc, scapula. 



depends mainly on his observations. It should be noted that the account of this bone 

 and of the femur given in the ' Geological Magazine ' (dec. 5, vol. iv., May 1907, 

 p. 202 *) is erroneous so far as these points are concerned. 



In the following description tlie limb is supposed to be in such a position that the 

 expanded paddle has its palmar (ventral) surface looking downwards and backwards, 

 and making an angle of about 45° with the vertical. 



The direction of the paddle with reference to the proximal end of the humerus is 

 marked in text-iig. SG by the line a-b, a being uppermost. In this case the border 



* See also Geol. Mag. [5] vol. v. p. 9G. 



