94 IXVEHTEBRATE ANIMALS. 



of tubular corallites, furnished with both tabul* and radiating septa, 

 and separated from one anotlierby an assemblage of smaller tabulate 



Fi;^'. 57. — Reil Coral (Ciimllinm rvhrviv), of the natural size, and a 

 portion enlarged. 



tubes, occupied l.iy rudimentary polypes. Along with the living 

 Heliopora of the Pacific and Indian Oceans, various ancient corals 

 {Heliolites, &c.) have been placed. 



Order III. Riigosa. 



This order merely requires 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 Zoanthana 

 sderodermata in having a well - develojied sclerodermic coiullum, 

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

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

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

 agree with the Alnjonixrut in having tlieir ])a,rt3 in multiples of 

 four, but differ from tliem in having a well-developed sclerodei'mic 

 condlum in which sej)ta are present. They are chiefly known as 

 fi.>.^sils in the older rocks of the earth's crust, and they have no un- 

 doubted representatives at the present day. 



