210 CEYLON PEARL OYSTER REPORT. 



maimer described by Pourtales and Duerden, and that it is only at a later stage of 

 growth that the extension of the cohunellar trabecular overspreads the union of the 

 tertiaries with the secondaries and causes the latter to appear as if they sprung 

 directly from the columella. The primary and secondary septa are much thickened 

 and porous towards their thecal ends. 



Balanophyllia socialis, Semper. Plate II., figs. 8 and 8a. 



Rhodopsammia socialis, Semper, 'Zeit. fur wiss. Zool.,' xxii., p. 260, 1872. 



A beautiful cornuate specimen from the pearl banks, Gulf of Manaar, clearly belongs 

 to this species, as is shown by its subcircular calice, deep fossa, well-developed and 

 projecting columella, and four fully developed cycles of septa. Its measurements are : 

 height 27 millims. ; calice 10 minims, x 9 millims. ; depth of calice 6 millims. There 

 are no buds, but a small outgrowth of the theca 3 millims. below the lip of the calice 

 on the opposite side to that drawn in fig. 8 is evidently the commencement of a bud. 

 The primary and secondary septa are equal in size, as described by Semper, and 

 their surfaces are covered with very fine granules ("ausserst fein gekornelt"), but 

 they are only very slightly thickened peripherally, and in this respect resemble 

 Rhodopsammia affinis, which, as Semper himself says, is probably nothing more 

 than a variety of R. socialis. R. dubia and R. incerta, both Semper, again are 

 almost certainly nothing more than varieties of the same species. Semper describes 

 the quaternary septa as uniting with the tertiaries close to the columella. In the 

 Ceylonese specimen, as is shown in fig. 8a, the quaternaries do not invariably unite 

 with the tertiaries, and indeed they follow M. Edwards and Haime's law very 

 closely, the quaternaries nearest the primary septa being, as a rule, the best 

 developed. The infrequent union between the third and fourth cycle septa, however, 

 does not indicate that the septa have not been developed according to Pourt ales' 

 and Duerden's law, for the latter author shows (10, p. 103, fig. 12, c) how the 

 bifurcated external limbs of the lower cycles of septa commonly become detached 

 from the inner limb. 



A dead and corroded specimen from deep water off Galle seems to belong to this 

 species. The calice was broken so much that its characters were indistinguishable, 

 hut a section taken lower down shows that it is peculiar in having a tetrameral 

 instead of a hexameral arrangement. There are four systems : the primary septa 

 are the largest, the secondaries are smaller, but pass direct to the columella, the 

 tertiaries also join the columella, but converge in a marked manner towards the 

 secondaries, and there is a complete fourth cycle uniting with the tertiaries. There 

 is no indication of this arrangement being derived from an originally hexameral 

 arrangement, and it must be regarded as a remarkable variation from the normal. 



Balanophyllia taprobanse, n. sp. Plate II., figs. 9 and 9a. 

 Height of corallum L5 millims. ; calice millims. x 5 millims. ; depth of calice, 



