26 



TABULATE CORALS. 



allies are Palaeozoic, Polytremacis is Secondary, while Helio- 

 pora commences in the Chalk and still survives. The true 

 affinities of this singular group of Corals were quite unknown 



Fig. II. A, Small colony of Helioliles megastoma, of the natural size ; B, Small portion of the 

 surface of the same, magnified, showing the calices of the large and small tubes (a and b) ; 

 C, Vertical section of the same, enlarged, showing the large tabulate corallites (a) and 

 the smaller tabulate tubes of the so-called crenenchyma (b). 



till Mr Moseley examined the living animal of Heliopora 

 c&rulea, from which he was enabled to prove conclusively 

 that Heliopora and its ancient relatives are truly Alcyonaria, 

 and not Zoantharia. The corallum in Heliopora ccerulea is 

 in all essential features entirely similar to that of Heliolites. 

 As in the latter genus, the corallites are tubular, with well- 

 developed tabulae, and having their walls folded in such a 

 manner as to give rise to a variable number (generally twelve) 

 of septal laminae. The ccenenchyma, so called, is composed 

 of slender tubes, of smaller size than the true corallites, packed 

 closely side by side, crossed, like the corallites, by regular 

 transverse tabulae, but destitute of septa. The soft parts 

 occupy only the parts of the corallum above the uppermost 

 tabulae, and therefore only a surface - layer of the colony is 

 actually alive. The polypes are completely retractile, with 

 eight pinnately-fringed tentacles and eight mesenteries. The 

 mesenteries, however, have no correspondence with the septa, 



