LIFE ON THE EARTH. 93 



series such as T. sacculus of the Carboniferous, T. 

 sufflata of the Permian, T. perovalis of the Fullers' 

 Earth, T. intermedia of the Cornbrash, T. biplicata 

 of the Green Sand, T. semiglobosa of the Chalk, 

 T. grandis of the Crag, and T. vitrea of the existing 

 ocean, illustrate each largely by examples with sinu- 

 ated or even margins, more or less prominent beaks, 

 greater or smaller foramina, we shall be amazed at 

 the small amount of real diiferences which divide 

 these species so far how very far! removed from 

 one another in order of time. If we try on a min- 

 gled series of Terebratulse of all ages the sharpest 

 powers of our differentiating naturalists, the same 

 result may happen to them as has happened to older 

 palaeontologists, to confound species differing in age 

 from the Devonian Limestones to the Upper Green 

 Sand; from the Chalk to the Bath Oolite; from the 

 Lias to the Mountain Limestone. Little difference 

 appears between T. striata of the Chalk and T. caput 

 serpentis of the Sea, nor is T. fimbria of the Inferior 

 Oolite very unlike the recent T. Australis. 



If we choose among Rhynchonellse a series such as 



R. decemplicata, Silurian ; R. anisodenta, Devonian ; 

 R. pleurodon, Carboniferous ; R. variabilis, Lias ; R. tetrae- 

 dra, Marlstone j R. media, Fullers' Earth ; R. obsoleta, Great 

 Oolite; R. inconstans, Kimmeridge Clay; 



or compare 



