94 INVERTEBRATE ANIMALS. 



of tubular corallites, furnished with both tabxilse and radiating septa, 

 and separated from one another by an assemblage of smaller tabulate 



Fig. 57. — Red Coral (CoraUium ruhrum), of the natural size, and a 

 portion enlarged. 



tubes, occupied by rudimentary polypes. Along with the living 

 Heliopora of the Pacific and Indian Oceans, various ancient corals 

 {Heliolites, &c.) have been placed. 



Order III. Rdgosa. 



This order merely reqviires mention, as almost all, or all, its mem- 

 bers are extinct, and are therefore only known to us by their hard 

 parts or skeletons ; while the true characters and limits of the group 

 are not completely worked out. They agree with the Zoantharia 

 sclerodermata in having a well - developed sclerodermic corallum, 

 but differ from them in the fact that the septa are typically in four 

 systems ; and there are generally transverse plates or tabulae com- 

 bined with the vertical plates or septa. On the other hand, they 

 agree with the Alcyonaria in having their parts in multiples of 

 four, but differ from them in having a well-developed sclerodermic 

 corallum in which septa are present. They are chiefly known as 

 fossils in the older rocks of the earth's crust, and they have no un- 

 doubted representatives at the present day. 



