XIV ZOANTHARIA MADREPORARIA 403 



cnemaria in many respects, and tlie Plesiofungiidae form a con- 

 necting link with tlie Astraeidae. It is very probable that this 

 section had a dual origin, and therefore does not represent a 

 single line of descent. 



Fam. 5. Plesiofungiidae. — This family is related .to the 

 Aporosa in the possession of septa that are generally solid 

 and imperforate, and to the Astraeidae in particular in the 

 possession of dissepiments. They differ from them, however, 

 in the presence of synapticula and in certain peculiarities of 

 the tentacles. 



The genus Siderastraea has recently been studied by Duerden.^ 

 The colony is usually massive and encrusting in habit. The zooids 

 when expanded do not rise much above the level of the corallura. 

 The tentacles are short and are arranged in irregular cycles on the 

 disc. They terminate in knobbed extremities, and those of the 

 inner cycles are bifurcated. The colour of S. sicleraea is reddish- 

 brown when alive. Siderastraea is found in shallow water on 

 the coral reefs, and is widely distributed. 



In Agaricia the colony is more foliaceous. The tentacles are 

 rudimentary or small. The colour of the living zooids is very 

 similar to that of Siderastraea. Epistrelophylhitn is a solitary 

 coral, from the Jurassic series, belonging to the family. 



Fam. 6. Fungiidae. — Fungia is an unattached solitary coral 

 of a flat disc-like shape with very numerous exsert imperforate 

 septa. It is frequently of considerable size (six to twelve 

 inches in diameter). On many of the coral reefs of the old 

 world it is extremely abundant, and consequently it is one 

 of the commonest corals of our collections. When alive the 

 corallum is almost hidden by the disc, which is studded all 

 over wdth very numerous long tentacles." The colour varies 

 in different species, but is usually brown. One species on the 

 Australian barrier reef, F. crassitentacidata, is of a dark olive 

 green colour, the tentacles terminating in white knobs. 



The free adult Fungias are derived from a fixed stock called 

 the trophozooid, from which the young Fungias are detached by 

 transverse fission (see p. 388). The thecal wall of the young 

 Fungia when detached from the trophozooid is perforated, but 



' "The Coral Siderastraea," Carnegie Inst. No. 20, 'Washington, 1904. 

 - The reader is referred to the excellent pliotograjihs of living Fungias in 

 Saville Kent's " Great Barrier Reef," 1893, pi. xxiv. i>. 160. 



