314 Dzvi'llcrs of the Sea and Shore 



But what forbidding shapes they had! In one remark- 

 able genus, the ichthyosaurians, the body was shaped 

 like that of a fish, the four limbs were developed into 

 paddles, and the tail was long and lizardlike but termi- 

 nated by a fleshy fin, as in the dolphin, save that it was 

 vertical. The large head was drawn out into a long 

 pointed snout, resembling that of the crocodile, and the 

 jaws were equipped with a series of powerful, conical 

 teeth set close together. The long and slender jaws 

 were strengthened to resist any sudden shock by being 

 composed of numerous thin, bony plates. These plates 

 also made the jaws light and flexible as well as giving 

 them great strength. A feature no less striking was the 

 pair of great eyes contained in the head. In some 

 species these organs were more than a foot in diameter; 

 and they were further remarkable from the fact that 

 they seem to have been fitted to accommodate them- 

 selves for vision in air or water as well as for changing 

 their focal distance while the creature was in the pursuit 

 of its prey. The apparatus, which could thus adjust the 

 sight to the needs of the moment, was in principle not 

 unlike that of a diaphragm in front of a camera lens. 

 It consisted of a circle of about twenty overlapping 

 plates surrounding the pupil, and as it was probably 

 capable of closing completely, it must have been of 

 service also in protecting the eyeball during diving. 

 With eyes like these, the ichthyosaurus obviously was 

 at a considerable advantage not only in discovering its 

 prey at great or little distances, but in the obscurity of 

 night and the depths of the sea. The masses of broken 

 bones and scales of contemporary fishes that have been 

 found under the ribs of these creatures make it plain 



