144: 



THE MIDDLE PAST. 



thousands of miles of rock-matter (as the nummulitic lime- 

 stone) owe their origin to the shell-like coverings of these 



1, Siphonia ; 2, Ventriculites ; 3 Manon ; 4, Scypliia ; 5, Textularia ; 0, Lituola: 

 7, Orbitoides ; 8, Rotalia. 



the lowest of animated existences. Corals, though occur- 

 ring in many genera (parasmilia, trocJiocyathus, &c.), are 

 by no means so abundant as in the oolite ; but star-fishes 

 (goniaster and oriaster) and sea-urchins (cidaris, diadema, 

 salenia, galerites, &c.) are obviously on the increase, and 

 the beautiful preservation of the latter constitutes one of 

 the most characteristic features of the chalk formation. 

 Encrinite life is now drawing to a close, and in a few species 

 of pentacrinus, Bourgueticrinm, and marsupites, carries 

 down the descent to the solitary pentacrinite of the existing 

 ocean. Annelids, like serpula and vermicular la, construct 

 their tortuous tubes in profusion, and in such a marine me- 

 dium barnacles (pollicipes and scalpellum) appear in greater 

 force than during any former epoch. In crustacean life, 

 the bivalved entomostraca are extensively represented by 



