CORALS AND CORAL-ANIMALS. 157 



simple linear series. The numerous tiiin, calcareous, radiating laminae or "septa" that form 

 the inner lining to each separate cup are, as compared with certain otherwise somewhat 

 approximate species, perfect!}' smooth-edged. The tentacles of the living polyps in this group 

 are, in their most fully-expanded state, also remarkable for their spherically knobbed or other- 

 wise conspicuously inflated terminations. This coral family, so far as it is represented m the 

 Great Barrier system, is exclusively confined to the warmest equatorial region, having been 

 obtained by the author most abundantl}' in Torres Strait and thence southward as far as the 

 Cairn Cross islands. Among the reefs opposite Cooktown, between latitudes of 15^' and 

 16° S., and in all localities investigated farther south, the Euphylliaceae are apparently 

 entirely unrepresented. 



In the Torres Strait district as many as three genera of the Euphylliaceous family have 

 been collected by the author. The most abundantly represented one among these three is the 

 typical genus Euphyllia, in which the matured coralla form hemispherical clusters, and the com- 

 ponent digitiform corallites, increasing by dichotomous subdivision, are more or less independent 

 at their distal or growing terminations. The dimensions of the hemispherical coral-masses 

 of this genus are not large ; their measurement, from the centre to the periphery, rarely exceeds 

 eight or ten inches, and they are in most instances much smaller. The expanded polyps in this 

 genus are among the most beautiful in the coral class, being surmounted by tufts of cylindrical ten- 

 tacles the extremities of which, in full extension, are knobbed like the head of a snail's horn or 

 drumstick, and of various colours. In the larger of the two species observed, Euphyllia glabrcscciis, 

 the tentacles vary more commonly from a rich seal-brown to a dark myrtle-green, the rounded tips 

 being white, blue-grey, or golden-yellow. In rarer instances the tentacles are a brilliant grass- 

 green, with pale lemon-yellow tips. In the second and smaller species, Euphyllia rugosa, the 

 tentacles are usually slate-grey or lilac, with brilliant emerald-green terminal knobs. An interesting 

 observation was made by the author, with reference to the variation in colour that may obtain 

 among the polyps belonging to the same colony-stock, or corallum, of Eupliyllia glabrcscciis, in 

 relation to the amount of light to which they are exposed. An example observed in the neighbour- 

 hood of Thursday Island was so growing, that certain of the polyps projected underneath and 

 were shut out from the light by surrounding coral growths. In this completely shaded position 

 the tentacles were transparently white with pale primrose-coloured tips. Where the light only 

 partially fell on them, the tentacles were sage-green with brighter yellow tips; while, throughout 

 the area fully exposed to the sunlight, all the tentacles were dark brown, with deep golden 

 terminations. Corresponding illustrations of the effect on the colours of coral-animals, produced 

 through the absence of light, were subsequently observed among the representatives of the 

 two genera Mussa and Galaxea, hereafter referred to. In all the genera named, the polyps 

 screened from light were similarly bleached, after the manner of cultivated sea-kale or celery. 

 Characteristic coloured illustrations of the polyps of the genus Euphyllia, in various conditions of 



