CORALS AND CORAL-ANIMALS. i6i 



occur. In other instances the entire living tissues are a deep rich brown, or brown and green 

 variously' blended ; while in one luxuriant species, Mnssa corymbosa, — whose separate corallites 

 may be eighteen inches long, and the entire corallum two or three feet in diameter, — all of the 

 component tissues are bright brick-red, and the extended tentacles a transparent tint of the same 

 colour. In the structure of their tentacles, the polyps of the genus Mussa differ in a marked 

 manner from those of Caulastr^a, and other species previously enumerated. Their essential 

 feature, in the expanded state, is typically illustrated by Fig. 3A of Chromo plate V., representing 

 a diagrammatic vertical section of an expanded polyp of Mussa corymbosa. As here shown, short, 

 acummate tentacles are developed in a fringe-like manner throughout the surface of the oral disk, 

 or peristome, while the extreme edge of this tentaciliferous area projects laterally — terminating in 

 section, in a fine point — to a considerable distance beyond the edge of the corallite. The short 

 acuminate tentacles thus exhibited in a linear series would seem to correspond with the coarse 

 serrations of the subjacent septa. The polyps of the green and brown Mnssa multilobata are 

 shown, under corresponding conditions of contraction and expansion, in Figs. 4 and 4A of 

 the same plate. In this species, however, the peristomial disk and associated tentacles, when 

 fully inflated by injected water, are, in the lightest coloured examples, very nearly transparent. 

 The genus Mussa is one of the most cosmopolitan types, being represented in more or less 

 abundance throughout the Barrier district. Several masses of the commoner brown species, 

 Mnssa multilobata, occupy a central position in the photographic view, Plate X., No. i, repre- 

 senting the fringing reef in the neighbourhood of the Palm Islands. A bleached corallum of 

 the same type is likewise included in Plate I. of the same series. 



A very distinct generic type, nearly allied to Mussa, but differing from it in the facts 

 that the mature corallum is detached and lies freely on the sea-bottom or surface of the reef, and 

 that the septal edges and external ridges, or costse, are very finely serrated instead of coarsely 

 toothed, is that of Trachyphyllia amarantns, represented in Figs. 1, ia, and b of Chromo plate No. 

 V. In its adult, detached, and pedicellated young condition of growth, the corallum of this genus 

 corresponds with that of Pectinia; but it does not attain to such large dimensions, rarely 

 exceeding five or six inches in diameter. The tentacles of the living polyps of Trachyphyllia 

 differ from those of Pectinia in being attenuate and transparent, like those of Mussa, but are 

 slightly inflated at their tips ; they are also similarly developed in a fringe-like manner throughout 

 the peristomial region. The membrane of the oral disk, and that covering the surrounding septal 

 edges in this species of Trachyphyllia, are liable to considerable colour variation. In some 

 specimens they are dark brick-red throughout, and in others elaborately variegated with shades of 

 green, brown, red, and yellow in diverse combinations ; but all these colours may co-exist in the 

 same corallum. The typical Barrier species, Trachyphyllia amarantus, has been obtained by the 

 author on exposed reefs near Warrior and Thursday Islands, and also, by dredging, in Cleveland 

 Bay, off Townsville, at a depth of three or four fathoms, but not farther south. 



