60 MADREPORAEIA. 



which tlie rosette of pali are the chief representatives of the iutracalicular skeleton. The 

 incipient rosette is distinct, bnt its elements are not pronounced. 



A similarly irregular cross striation of the walls by the tops of the septa may be seen in 

 Goniopora G-reat Barrier Eccf S (PI. III. fig. 3), but the skeletal elements are there thicker 

 and coarser, and the rosette formation is entirely confined to the lateral caUcles. 



a. Zool. Dept. 92. 1. 16. 31. 



Presented by the Lords of the Admiralty. 



28. Goniopora North-West Australia (6,2. (I'l. IV. fig. 1 ; PI. XI. fig. 15.) 

 [Bassett-Smith Shoal, Holothuria Pieef (9 fathoms), coll. Bassett-Smith; British Museum.] 



Description. — Corallum explanate, variable thickness, 2-4 mm., with smooth wavy 

 surface, encrusting edges 1-2 mm., bent under (? seldom free). 



Calicles very small, faint, shallow depressions, l'5-2 mm. across, of indefinite shape, 

 mostly polygonal, with minute central fossa. The whole surface a compact mosaic of very 

 minute granrdes. The walls slightly raised, solid looking and covered with minute frosted 

 flakes and granules ; the septa slope down from the wall-ridges. The long narrow interseptal 

 loculi, though running right to the ridge between adjoining calicles, seldom pass into one 

 another. The compact septa consist of 24 radial series of granules. The primaries with as 

 many as 5-6 in a series, and all of tliem so arranged as sometimes to allow the intervening 

 spaces to form concentric rings round the fossa. The arrangement of the granules further 

 sliows the typical septal formula, with its proper fusions. They slope, as a rule, evenly down 

 towards the fossa, but here and there faint traces of a central boss can be seen. 



The texture in section is very close and dense, but composed of very delicate skeletal 

 trabeculfe, the tips of which form the granules. 



But for the presence of the 24 septa arranged in the typical formula, this might be taken 

 for a Porites. Its label bore the provisional name Poritcs arenosa. It is quite an extreme form 

 among known recent Goniopores, although when more forms from deeper water are known its 

 specialisation may be found to be common. See observations under the next form. On 

 the correlation of its type of calicle with the thin explanate growth, see Introd., pp. 23 and 24, 

 and Table IV. p. 178. The diminution in size of the calicles, coupled with the retention of 

 the full septal formula, is a point of interest when the origin of Porites from Goniojiora by a 

 process of reduction in the number of septa is taken into account. It shows that the reduc- 

 tion need not necessarily be an adaptation to diminished size. (Cf. Introduction, p. 21.) 



Equally interesting, too, are the possible relationships between this form and the three 

 following. They suggest a series, although there should be some intermediate form between 

 this and the next to make it complete ; on this series see p. 63. 



a. Zool. Dept. 92. 1. 16. 45. 



Presented by the Lords of the Admiralty. 



