CORALS AND CORAL-ANIMALS. 187 



clear liver-brown throughout, with the exception of white tips to the tentacles. The tentacles 

 which are invariably twelve in number, are in their most characteristic extension, inflated at their 

 extremities. Representations of the living coralla and polyps of two of the afore-named species 

 are included in Chromo plate No. VIII., while the growing coralla of Alveopora viridis form 

 conspicuous objects in the foreground of the photographic reef-view No. XXXIII. a. 



A genus of the Perforata, closely allied to Alveopora, is that of Rhodarasa. The corallum in 

 this generic group, however, is of much more dense consistence, and the polyps possess twenty- 

 four tentacles, in place of twelve only ; these tentacles, moreover, are never capitate. The 

 corallum of Rhodarasa is almost invariably hemispherical or lobate in contour, and both its 

 surface and the associated polyps exhibit a great diversity of colour. A bright apple-o-reen 

 tint like that of Alveopora sometimes obtains. In other species, the polyps may be pale green 

 with lilac-tipped tentacles, or lilac with white oral centres and tentacle tips ; while in a third 

 variety they are clear liver-brown throughout. A conspicuous colour variation of the commonest 

 Barrier species, Rliodarcca calicularis, is represented by Figs. 6 and 6a of Chromo plate No. VI. In 

 this example the protruding oral centre is bright crimson, and the surrounding peristomial area pure 

 white ; the tentacles are a deep sage-green, and the shaft or column of the extended body is lio-ht 

 brown. A new species of this genus, Rhodarcea fruticosa, obtained by the author on the Warrior 

 reef, differs from previously described allies in that the corallum takes the form of a small, 

 erect, furcately-branching bush. The polyps of this species are clear liver-brown, with a pure 

 white oral disk. As originally described by the author in the Records of the Australian 

 Musettin (Vol. I., No. 6, p. 123, 1S91), this species was referred, under the above specific name, to 

 the genus Goniopora. It is a feature common to all the species of the genus Rhodaraea, and to 

 those of Alveopora, that the polyps in full extension protrude a long distance beyond the orifices 

 of their individual corallites. The tentacular wreath under these conditions is mounted on the 

 extremity of a slender, cylindrical, stalk or column, which may project for the length of an inch 

 or more from the surface of the corallum, and, together with the attenuated tentacles, float loosely 

 in the passing current. The fact is made clear in this association that the corallum in the Madre- 

 poraria is secreted entirely by the basal region of the polyp's body. It is worthy of note that 

 the polyps of Rhodaraea correspond structurally with those of the aporous genus Heliastrcea, in 

 the same manner as the polyps of Porites have been shown to resemble those of Stylopora. 

 Typical illustrations of the living coralla and associated polyps of several species of Rhodaraea 

 are included in Chromo plate No. VI. 



Among the genera of Perforate Madreporaria that remain to be noticed, Turbinaria is remark- 

 able for the elegant cup- or vase-like contour of the coralla of its most characteristic species. 

 When not vase-shaped, the coralla form more or less extensive smooth, or plicated, folia, or more 

 rarely, incrusting masses. Known by the popular title of Cup-corals, two species, Turbinaria pcltata 

 and T. patnla, are commonly obtained by the pearl-shell divers of Torres Strait, attached to 



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