183 SKETCHES OF CREATION. 



I hasten to the conclusion of my sketch. This reptile- 

 producing age of the world was fruitful in the varied forms 

 of gigantic lizards and crocodiles. To the former belong 

 DurydoTus serridens, and probably Scmropus primcevus of 

 the New Red Sandstone of Pennsylvania, and Bathygna- 

 thus borealis (as before stated) of similar rocks in Nova 

 Scotia. The crocodiles of the earlier epoch of the Jurassic 

 Age came upon the earth in herds. They mostly possessed 

 the peculiarity of having their vertebrae concave before and 

 behind, like those of fishes a character for which the term 

 amphiccdian has been invented by Owen. A few, as the 

 Streptospondylus, were exceptional among vertebrates, in 

 having their vertebrae convex before and concave behind 

 (opisthoccelian), while the rule among all existing animals 

 of this family is to have the vertebras concave before and 

 convex behind (proccelian). 



The most gigantic of all reptiles that ever crawled over 

 the face of the earth or swam in its waters were those of 

 the family of Dinosaurians, whose elongated and ponder 

 ous forms must grace the picture of Oolitic and Wealden 

 scenes. Of these, the Megalosaurus was the advance guard, 

 and measured forty feet in length. The Iguanodon and 

 Pelorosaurus followed in the Wealden epoch, the former of 

 which was sixty feet in length and the latter seventy! 

 Turtles, the highest order of reptiles, made their advent in 

 small numbers toward the close of. the Jurassic Age, but 

 never flourished in abundance till after the reign of gigan 

 tic saurians. Just as the curtain was falling on the scenes 

 and actors of this wonderful drama of reptilian life, two or 

 three small mammals ran upon the stage, and gave them 

 selves up to extinction barely in time to enable us to say 

 that the highest class of vertebrates added its contribution 

 to the animal variety of that period in which the Alps were 

 accumulating as sediment s in the bottom of the sea. We 



