1 10 MANUAL OF ZOOLOGY. 



(fig. 31, a}. The more important variations of detail which 

 occur in both classes of corals will be noticed under the differ- 

 ent families in which they occur. It only remains to add that 



Fig. 31. Sclerodennic and Sclerobasic Corals, a Portion of branch of Dendrophyllia 

 nigrescens, a sclerodermic coral (after Dana) ; b Longitudinal section of I sis 

 hippuris, a sclerobasic coral, exhibiting the external bark or ccenosarc, with its im- 

 bedded polypes, supported by the internal axis or skeleton. (After Jones.) 



doubt has been thrown by eminent zoologists upon the valid- 

 ity of the general distinction between sclerobasic and sclero- 

 dermic corals, as above defined. 



Returning now to the Zoantharia Sclerobasica, we find the 

 sub-order to contain the two families of the Antipathidce and 

 the Hyalonemadce. (or Hyalochfftida). Of these the Antipathidcz 

 are chiefly noticeable because of their likeness to some of the 

 Gorgonidce, from which, however, they are readily distinguished 

 by the fact that the number of their tentacles is a multiple of 

 six, whereas in the latter it is a multiple of four. Antipathes 

 itself possesses a horny sclerobasic corallum, which may be 

 simple or branched, and is covered with numerous small 

 polypes, united together by a ccenosarc, and possessing six 

 tentacles each. 



The second family, that of the Hyalonemadce, contains the 

 so-called " Glass-zoophytes," the true nature and position of 

 which has been a subject of much controversy. By Dr Gray 

 the HyalonemadcR are believed to be true Actinozoa, and he 

 defines them as follows : " Social Zoanthoid polypes secreting 

 a central, siliceous, internal, axial coil for their support. The 



