THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. II. 



No. IV.— APRIL, 1915. 



OZRIG-IlSr.A.1-, .A-IRTIOZHilES. 



I.— T Note on a Mounted Skeleton of Ophthalmosaurus icenicus, 



Seeley. 



By C. W. Andrews, D.Sc, F.E.S. (British Museum, Natural. History). 

 (PLATE V.) 

 (Published by permission of the Trustees.) , 



ONE of the most important additions recently made to the Gallery 

 of Fossil Reptilia at the Natural History Museum, is a mounted 

 skeleton of the highly specialized Ichthyosaur known as Ophthalmo- 

 saurus zcenicus, Seeley. This reptile presents many peculiarities, 

 for the most part indicating a very high degree of adaptation for 

 life in the open sea and for rapid movement through the water, 

 probably sometimes at considerable depths. In fact, Ophthalmosaurus 

 may be regarded as representing among the Reptilia the swiftly 

 swimming toothed-whales among the Mammalia, and it is interesting 

 to note that the similar mode of life in the two cases has produced 

 - in some respects similar modifications. Thus the front paddles are 

 enlarged, the hind ones reduced ; in whales the latter have disappeared 

 altogether. Again, there was a large caudal fin, vertical in this 

 case, and the head was elongated, the snout sharp, and the neck so 

 short as to be practically non-existent. The enlargement of the 

 fore-paddles is brought about by the presence of a very large pisiform 

 bone, which together with the radius and ulna articulates with the 

 humerus, thus forming a very broad base for the expanded terminal 

 portion of the paddle. Another striking peculiarity is the great 

 induction of the dentition, the teeth in the adult being very small 

 and confined to the front of the jaws. Baptanodon, an American 

 form very closely allied to, if not identical with, Ophthalmosaurus, 

 was for a long time regarded as toothless. This reduced dentition, 

 so unlike what is usually found in members of the group, must 

 indicate some considerable change in the nature of the food, but what 

 this was is unknown. 



This specimen has been mounted with great skill and neatness by 

 Mr. L. T. Parsons, so that any portion can be removed for examination 

 without much difficulty. It is made up almost entirely from portions 

 of three individuals : the mandible and skull, except the occipital 

 region belong to one (R. 3702) ; the occiput, the sclerotic rings, the 

 vertebral column nearly to the bend of the tail, the ribs, shoulder- 

 girdle with the fore-paddles, and the femora to a second (R. 3893) ; 

 while the remainder of the caudal region was supplied by a third 

 decade vi.— vol. ii.— no. rv. 10 



