416 



LOWER VERTEBRATES. 



in outline a shape not unlike that of a rounded elm leaf. This structure is very 

 characteristic and has been of considerable value to geologists, as, on finding teeth of 

 a similar nature in several of the Dinosaurs, they are ujsheld in inferring that these 

 extinct forms had many points in common with the more recent. 



Mr. Darwin gives a most interesting account of the lizards of the genus Amhly- 

 rhynchus. These animals are restricted to, and characteristic of, the Galapagos 

 Islands, a small archipelago lying on the equator, five or six hundred miles west from 

 the Pacific coast of South America. The generic name has been given to these pecu- 

 liar reptiles because of their abbreviated snout, the head being formed like that of 

 some of the sea-turtles, and though the two species are both vegetable feeders, and 



Fig. 240. — Amblyrhyiwhus cristatus, Galapagos lizard. 



ai-e acknowledged to be of the same genus, they are of the most opposite habits, one 

 being purely marine, never retreating but a few feet from the shore, and feeding exclu- 

 shely on seaweeds, while the other is terrestrial, feeding on cacti and acacia leaves. 



A. cristatus, the marine representative, is very abundant on all the islands of the 

 group, in some situations so congregating as they lie basking in the sun as to almost 

 line the rocks along the shore. Though allied to the iguana, the tail is laterally 

 compressed and serves as the chief organ of locomotion, as the animal by horizontal 

 flexions of its body, propels itself through the water ; the limbs, with the partially 

 webbed toes, being appressed to the sides and only used to give an occasional push 

 as the animal glides along near the rocky bottom in search of the soft green 



