THE CRUST OF THE EARTH. 

 70. THE Spondylus, figs. 16, 17, of which there are forty-five 



Fig. 16. Fig. ir. 



Spondylus Spinosus. 



fossil species, first appears in the lowest stratum of the cretaceous 

 group, and presents an example of the fossil Lamellibranchise. 



71. The Pentamerus, figs. 18, 19, of which there are twenty- 

 one fossil species, is an example of the Brachiopoda. This is 



Fig. 19. 



Peutamerus Kuightii. 



first seen in the lowest strata of the silurian group, and becomes 

 extinct after the Devonian period, so that its existence was 

 limited to the earliest epochs of animalisation. 



72. The Reticulipora, figs. 20, 21, 22, 23, an example of the 

 Bryozoares, is an extinct genus Retepora, of which there are five 

 fossil species known ; the first in the middle strata of the oolites, 

 and the others in the upper strata of the cretaceous group. In 

 this the meshes are formed of high vertical laminae, supplied 

 with cells by transverse lines on each side ; fig. 20 shows the 

 whole in its natural size; fig. 21, the external part magnified; 

 fig. 22, the internal part magnified ; fig. 23, the laminse as shown 

 with a still higher magnifying power. 

 66 



