492 MESOZOIC TIME REPTILIAN AGE. 



far as now known, affords no evidence of the existence of the pre- 

 sent cool temperature in the waters of the temperate zone. 



The corals of the Cretaceous beds in England and Europe are so 

 closely related to the reef-forming species of the present seas, that 

 these concur with the other testimony in favor of warm seas. 

 Moreover, as such reefs reach now to about the parallel of 27°, the 

 coldest temperature of these regions, which is near 68° F., was 

 probably the coldest temperature of the waters of the German 

 Ocean, New Jersey shores, Mississippi basin, Vancouver's Island, 

 Chili, and Straits of Magellan. They were within what is called 

 the sub-torrid zone on the map of oceanic temperature. 



The present position of the winter line of 35° F. on the Physio- 

 graphic chart is probably near that occupied by the line of 68° F. 

 in the latter part of the Cretaceous period. 



There is a difference in the later Cretaceous between the species 

 of northern and southern Europe, and also between those of the 

 northern and southern United States, as explained on page 479, 

 and this difference has been attributed to diversity of tempe- 

 rature. Some diversity of this kind undoubtedly existed; and it 

 should be apparent in the fossils. But the particular facts re- 

 ferred to may not be sufficient to prove it. In North America, at 

 least, the peculiarities in the life of the two regions, Texas and 

 the Upper Missouri, may be owing rather to the difference in the 

 horizon of the beds, and also to that of clearness or purity of the 

 waters (Meek). 



5. Life. — 1. Retrospective characteristics [allying the Cretaceous with the 

 preceding period) . 



1. Among Plants. — A preponderance of Conifers ; numerous Cycads. 



2. Among Radiates. — Crinoids of the Aj)iocrinus family and others. 



3. Among Mollusks. — The genera Thecidea, Gryjihsea, Exogyra, Inoceramus, 

 Trigonia, Nerinsea, Ammonites, Belemnites. 



4. Among Vertebrates. — Pycnodont Ganoids, Cestraciont and Hyhodont 

 Sharks, Dinosaurs, Enaliosaurs, Pterodactyls. 



5. Species of plants and animals all extinct. Of the genera of plants only 

 one-twentieth living; of the genera of Cephalopods, only one-twentieth; of the 

 genera of fishes arid reptiles, only one-sixth. 



2. Characteristics peculiar to the Cretaceous. 



1. Among Protozoans. — Great multiplication of genera and species of Rhi- 

 zopods and Sponges. 



2. Among Radiates. — Echinoderms of the genera AnancJiytes, Galerites; 

 Crinoids of the genus 3tarsnpites. 



3. Among Mollusks. — Species of Exogyra and Inoceramus very common; 



