CORALS AND CORAL-ANIMALS. 167 



were by such crowding compelled to assume a polygonal shape. Finally, in these abnormally 

 crowded areas the septal divisions between the adjacent corallites were wanting, and they were 

 united together in a linear series, after the manner of a Cceloria or Meandrina. The colour that 

 would appear to be almost universally represented in the living coralla of the genus Favia is that 

 of a light-straw or lemon-j'ellow, sometimes variegated with a lesser amount of green or brown 

 The tentacles of the extended polyps, like those of Goniastraea and its allies, are completely colour- 

 less, and expand chiefly at night. The natural tints of the living corallum of a species of 

 Favia apparently identical with F. auiiconiin is represented by Fig. 14 of the Coloured Plate 

 No. V. In No. 6. of the same plate a second variety, very closely allied to Favia Bowerbanki, 

 is similarly depicted. 



Leaving for a while that typical section of the Astrasaceae which is characterised by the 

 production of more or less massive coralla, some attention may be directed to a few mem- 

 bers of the group that exhibit a somewhat abnormal structural plan. Certain of these, known 

 as the Lettuce-corals, Tridacophyllias, are characterised b}' the construction of coralla which 

 take the form of coalescing foliaceous expansions of paper-like tenuity and exceeding brittleness, 

 and that in certain species present a by no means remote likeness to leaves ot the lettuce and 

 endive tribe. This resemblance is more especially sustained among such species as Tridacophyllia 

 laciniata, illustrated by Fig. 1 2 of Chromo plate V., in which the predominating hue of the 

 corallum is a brilliant green. In other examples of the same species, as depicted in Fig. 13 of the 

 same plate, a bright golden-yellow represents the prevailing tint. In both varieties the edges of 

 the paper-like folia were white or yellow, or a very pale tint of the characteristic ground hue. 

 The polyp centres in this genus are almost exclusively confined to the oasis of the deep cups 

 or valleys formed by the surrounding elevated folia, and are stationed either singly or in 

 sparsely-scattered serial order. Living specimens of these Lettuce-corals, preserved for some 

 days in improvised aquaria, failed to reveal the possession by the polyps of tentacles other 

 than of a very minute and rudimentary description, which were developed only on the edges of 

 the septal ridges in the near neighbourhood of the mouth. The region of the mouth, it should be 

 mentioned, in the condition of fullest expansion observed, is elevated, as indicated in the figure- 

 named, in the form of a distinct cone, or hypostome. In accordance with the writer's investiga- 

 tions, the members of the genus Tridacophyllia are essentially characteristic of the Mid-Barrier 

 district, being especially abundant in the neighbourhood of the Palm Islands and Port Denison. 

 Fully-developed coralla of the species here illustrated not unfrequently form foliaceous clumps, a 

 foot or more in diameter ; but, as usually found growing on the tidally-exposed reefs, they more 

 commonly attained to only half that size. 



In addition to the species, apparently identical with Tridacophyllia laciniata, above described, 

 a very distinct form of the same genus occurs in some abundance on the Palm Islands reefs. In 

 this type, the edges of the septa pertaining to the two primary cycles exhibit a strong tendency 



