484 MESOZOIC TIME. 



folded, even to its highest tribe, that of Hymenopters, species of this 

 group, related to the bee, having occurred. 



Vertebrates. — Fishes. — Ganoids and Selachians (or fishes of the 

 Shark tribe) continued to be predominant kinds through the era ; but 

 the higher type of Teliosts (or common osseous fishes) appeared in 

 the Jurassic, and included many species in the Cretaceous. 



The Ganoids lost, in the Triassic, the Paleozoic feature of verte- 

 brated tails ; and this is a mark of progress ; for it is an example of 

 that abbreviation of the posterior extremity which generally marks 

 elevation in grade as well as progress in embryonic development. In 

 the Jurassic period, the number of species of Ganoids reached its 

 maximum, and also the diversity of generic forms ; and this therefore 

 was their period of culmination. The Ganoids are at present nearly 

 an extinct tribe. 



The tribe of Sharks was numerously represented by large species 

 of the Hybodont, Cestraciont, and other groups ; and the family of 

 Cestracionts, those having a pavement of bony pieces in the mouth, 

 for mastication, appears to have passed its maximum in the Creta- 

 ceous : it is now nearly extinct. But the highest species of the Sela- 

 chians existed later in the Tertiary. 



Reptiles. — The scale-covered Amphibians, called Labyrinthodonts, 

 which first appeared in the Carboniferous age, had gigantic species in 

 the Triassic, and none afterward, so far as known. The type of 

 Amphibians therefore culminated in the Triassic, the Labyrinthodonts 

 being its highest species. We have now among Amphibians only the 

 little, naked-skinned Frogs and Salamanders. 



Of true Reptiles, all the grand divisions of the class were displayed ; 

 and the type culminated in this era. 



The Enaliosaurs or Swimming Saurians of the Triassic — the 

 Nothosanr type — had the open skull of a Batrachian ; but, in the 

 Jurassic, the group rose to the higher grade of the Ichthyosaurs and 

 Plesiosaurs ; and there were several genera and numerous species : 

 with the Cretaceous, the species disappeared. 



The Lacertians commenced, perhaps, iu the Carboniferous, and the 

 Crocodilians in the Permian, in species with the ichthyic characteristic 

 of biconcave vertebra?, and retained it through the Triassic and in some 

 Jurassic species. In the Jurassic and Cretaceous, the Crocodilians came 

 forth in many other species of great size, without this low feature. 



Snake-like Reptiles occurred, of enormous size, in the Mosasaur 

 tribe, and with articulated jaws, precursors of our modern smaller 

 snakes. 



The Saurian type in the Jurassic rose to the grade of Dinosaurs, 

 the highest in rank, and among the largest of Reptiles ; and these all 

 disappeared, by or soon after the close of the Cretaceous period. 



