74 CORALS 



inner cycles, becomes bifurcated, each brancli terminating 

 in a knob armed with batteries of nematocysts ; the other 

 tentacles are simply digitate. The colour of the polyps 

 varies according to the position of the colony on the reefs. 

 If they are not exposed to the sun they may be colourless, 

 but elsewhere they vary from light to dark brown. The 

 oral disc may show radial streaks of velvety green and the 

 angles of the mouth and the knobs of the tentacles are white. 



The following genera belong to the section of the family 

 sometimes called the Lophoseridae. 



Agaricia. — This coral forms colonies which are usually 

 foliaceous in growth, the calices arranged in irregular con- 

 centric rows on the upper or, more rarely, on both sides of 

 the leaves (Fig. 28). The rows of calices are separated by 

 prominent thecal ridges. The calices are small, 3-4 mm. 

 in diameter. The septa are numerous, as in other Fungiidae, 

 but do not extend from the margin as close to the centre 

 of the calyx as they do in Siderastraea, and consequently 

 leave a deeper and wider oral pit. The sides and margins 

 of the septa are profusely tuberculate, and in the depths of 

 the interseptal spaces the tubercles meet to form synapti- 

 cula. Asexual reproduction is by fission. 



Agaricia seems to be a widespread but not very common 

 coral on both East and West Indian coral reefs. In Jamaica, 

 according to Duerden, the colonies occur in shady places 

 at a depth of from 3 to 4 feet downwards, and are of a con- 

 spicuous bright reddish-brown colour. The tentacles are 

 rudimentary, from ten to eighteen in number, and widely 

 separated. In the state of contraction this coral resembles 

 other members of the family in that the polyp walls are 

 not folded over the oral disc. In the state of expansion, 

 emerald green circles can be seen surrounding the mouth 

 on the oral disc. 



As in many other corals in which asexual reproduction 

 is by fission, there are no directive mesenteries in the polyps. 



Pavona. — The genus Pavona, which belongs to the same 

 group as Agaricia, does not occur in the West Indies but 

 is fairly common on some of the Indian Ocean and Pacific 

 reefs. It differs from Agaricia in having much less prominent 



