INDIAN OCEAN PORITES. 207 
207. Porites Ceylon w@a)11, (P. Ceylonica wndecima.) 
[Ramesvaram, Pearl Bank, coll. E. Thurston ; British Museum. ] 
Description.—The corallum is like the last, but more smoothly convex. 
The calicles are pitted and conspicuous. The walls are reticular, very irregular in 
thickness and texture, the reticulum being fluent—that is, with no traces of any formal 
arrangement of the elements. The pores are smooth, round or oval. The reticular character 
of the walls extends to the intra-calicular skeleton also, which loses almost all traces of radial 
symmetry, and is seldom at the same level across any calicle. All the superficial parts of the 
ealicle skeleton can be seen, but confused; stray septa, a few pali, a columellar tangle, 
large interseptal loculi, can all be made out, but with so little symmetry that the skeleton 
appears to be a confused tangle. 
This specimen is puzzling ; it looks as if it might be a weather-worn specimen of the last 
form. Perhaps the shell had long been cast away in the Pearl Camp. The same elements 
can be seen in the two, but in this the finer surface details may have been lost. The walls 
stand up, and the calicles are very irregularly deepened, as if the deepening might have been 
due to the irregularity of the weathering. 
The greater fluency of the wall reticulum and the increased irregularity of the calicular 
skeleton, however, are differences of importance, and even though the skeleton has lost the 
glassiness of fresh material, and shows the opacity and chalkiness of a weather- or water-worn 
coral, the fine details of structure are so well preserved as to justify the belief that we still 
have the original surface. 
a. Zool. Dept. 90. 6. 20. 8 (part). 
208. Porites Ceylon (9912, (P. Ceylonica duodecima.) (Pl. XXXI. fig.3; Pl. XXXV. fig. 17.) 
[Ramesvaram, Pearl Bank, coll. E. Thurston ; British Museum. | 
Description.—The corallum not only encrusts the upper surface of the pearl shell, but may 
even send out free, explanate edges 2 cm. beyond it. The topmost surface tends to rise into 
irregular mammille about 1 cm. high and 1 em. thick. The free edges are thin, 1 mm., tend 
to droop, and even to fold under. 
The calicles are small, from 0°75 to 1 mm. across, deep, and as if punctured into the 
surface, though not neatly, but with ragged, irregular edges. The walls are of very irregular 
thickness ; they thicken in small groups, which then tend to rise up and form the mammille ; 
the wall at its thinnest consists of a single, very irregularly zigzag lattice-work, and at its 
thickest of an open reticular arrangement of such a lattice-work, which may be simply a stout 
reticulum, or have an appearance of flakes curving outwards into the horizontal. The vertical 
elements may also appear as flakes, the edges of which stand sharply up either as a reticulum 
or crossing the top of the wall as thin strie, mostly, but not always, radially arranged. 
