﻿118 MADREPOKAEIA. 



Ccenenchyma shows in sections a thick, basal, soUd layer, a dense and not pronounced 

 streaming layer ; the trabecular of the thickening layer are from 5 to 7 mm. in length. They 

 are stout and nodulate, and joined at regular distances by thick junctions, round or oval pores 

 being left which are largest near the surface, i.e. where the trabecule are thinner and the 

 ccenenchyma less dense. Where the trabecule rise above the surface as tubercles, their tips 

 are ragged but not swollen or bushy ; some rise higher than others, and become clear, solid 

 knobs which begin to join with the adjacent tubercles in the ty^^ical manner for the thickening 

 of the ccenenchyma. On the smooth side of the corallum the projecting trabeculse axe not so 

 apparent as tubercles, they appear more as the rough ends of the threads of the reticulum. 



There is only one specimen of this type. On account of the length of the trabecule, I 

 was disposed to unite it with M. solida, which I have, however, now transferred to the 

 glabrous group. The corallum consists of two bosses of thick coral which appear to be 

 encrusting the remains of a Madrepore. We have, unfortunately, no means of ascertaining 

 what the shape of a large specimen would be. It is possible that M. cactus may spring from 

 such a young stage, but the tubercles of M. cactus are much more highly specialised. 



a. Capricorn Island, Great Barrier Eeef. CoU. Saville-Kent. (Type.) 



95. Montlpora cactus. (PL XXI. fig. 5 ; PI. XXXIII. fig. 16.) 



Description. — Corallum rising into a tliick cylindrical upgrowth (at least 20 cm. high), 

 giving off a few thick, knob-like branches. The growth is of about the same thickness all the 

 way up, 2 to 3 cm. except where branches are growing out. The basal portion dies away 

 but is covered over by a living layer, while the branches of other corals with which the 

 rising column comes in contact are grown round and perhaps utilised for extra support. 



The calicles are conspicuous, deep, open, neatly star-shaped, • 75 mm. in diameter, with six 

 short tliick septa reaching to about the half radius circle, with traces of a second cycle ; two 

 dii'ectives generally visible to the naked eye ; irregularly distributed on the bulging portions 

 of the surface, where they may be 1 to 2 mm. apart, but crowded in depressions. Aperture of 

 the calicles as a rule well defined. 



Ccenenchyma shows, in section of the stem, a laminate axial strand of open reticulum from 

 which stout trabeculfe, 7 to 8 mm. long, radiate outwards, densely packed towards the centre 

 but wider apart towards the surface. These are joined together by stout cross bars, in marked 

 contrast to the thin spines which form the septal series seen in longitudinal sections of 

 calicles. Above the surface of the interstices these trabeculce rise as rounded tubercles, looking 

 solid but finely frosted to the naked eye, but under the lens seem to be covered with fine flam- 

 ing points. They seem to be best developed in the most protected places, where they are 

 about 1 mm. thick and 1 mm. high, and so crowded and compact as quite to obscure the true 

 interstitial surface. Here and there tubercles form flat plates as if two had joined together. 

 ISTo conspicuous tendency to form rings round the calicles. The tubercles are much more 



