THE COMANCHEAN PERIOD 739 



history of the plant kingdom. The precise time and place of 

 origin of the angiosperms is not known, but present data point to 

 the borders of the north Atlantic as the place of origin, and the late 

 Jurassic or earliest Comanchean as the time. 



About 400 species of Comanchean angiosperms are known from 

 the Atlantic coast. They were in a minority in the lowest Potomac, 

 but increase to an overwhelming majority in the upper beds. The 

 earliest forms are ancestral, but not really primitive, and throw 



Fig. 501. FRESH- WATER FAUNA OF THE COMANCHEAN (Lower Cretaceous) 

 from Montana, a and b, Pelecypods: a, Unio farri Stanton; 6, Unio 

 douglassi Stanton; c-e, Gastropods: c, Viviparus montanensis Stanton; 

 d, Goniobosis (?) ortmanni Stanton; e, Campeloma harlowtonensis Stan- 

 ton. (Stanton.) 



little light on the derivation of the group. The majority bear 

 definite resemblances to modern genera and some (as Sassafras, 

 Ficus, Myrica, and Aralia) are referred to living genera. Before 

 the end of the period, figs, magnolias, tulip trees, laurels, cinnamon 

 id other forms referred to modern genera, but not to modern 

 jies, had appeared. The cycadeans had dropped to an insig- 

 lificant place, and the conifers and ferns, while not equally reduced, 

 were subordinate to the angiosperms. 



The land animals. The aspect of the vertebrate life was inter- 

 lediate between that of the Jurassic and Upper Cretaceous, and, 

 far as it is known, has been sketched already (p. 720). Little is 

 :nown of other forms of terrestrial animal life. 



The fresh-water fauna. The molluscan fauna of the inland 

 raters had assumed a pronouncedly modern aspect, as illustrated 

 in Fig. 501. It had probably attained considerable importance 

 bhrough the extension of the fresh waters, but the record is by no 



