40 MADREPORARIA. 



as it is flaky. This passes gradually into a cortical layer, which is also irregularly reticular 

 and only dimly shows a tendency of the elements to bend out radially towards the surface in 

 wavy lines. No distinctly trabecular or concentric elements appear. 



In addition to the chief fragment above described, which allows so much of the original 

 character of the coral to be seen, are two fragments worn down beyond recognition except 

 that the section resembles the section of a, and the surface is not unlike the surface of the 

 basal tip of a, which had also been worn down quite thin. This coral is quite distinct from 

 the last, although in its thin, tall growth-form it seems to lead on to it. Of. also the next 

 form. 



a. With a longitudinal section and a microscopic slide. Geol. Dept. E. 2194. 



h. c. Two worn fragments probably of the same. Geol. Dept. E. 2551 and 2552. 



18. Porites Barbados 8. {P- Barbatce octava.) (PI. IX. fig. 2, right hand figure, and 3.) 

 [Low level reef, near Bridgetown, colL Bishop Mitchinson ; British Museum.] 



Description. — The corallum forms tufts of small, smooth branches varying greatly in 

 thickness not only among themselves (some being round and only 9 mm., and others slightly 

 flattened and as much as 15 mm. in longest diameter) but also along their lengths owing to 

 slight fusiform thickenings alternating with gradual constrictions. The forkings are at small 

 angles, but apparently irregularly, the branches occasionally fusing together. 



The calicles are very small, under 1 mm., and for some 3 cm. below the tips quite 

 ill-defined, that is without any walls visible at the surface, the interseptal loculi of adjacent 

 calicles running continuously into one another. This character seems to pass away owing to 

 the columellar tangle sinking below the level of the wall region, which then forms a ridge, 

 along which a thread may sometimes run, at others the septal striae rise above the flaky 

 texture of the wall, and between these striae the interseptal loculi communicate freely. 



In addition to the specimen a, which distantly resembles P. Barbados 4-, at least in 

 growth-form, there is a long wavy fragment, 6 cm. long and 1 cm. thick, which may be of the 

 same kind. I would suggest that it may have been stimulated to extra growth in length by a 

 worm twining its calcareous tube up one side of it. The actual tips of both have been broken, 

 but it would appear as if the two had raced upwards to try and top one another. The stem 

 shows great irregularity in thickness as if its normal growth had been interfered with, and 

 its living surface to have been prejudicially affected by, the worm at different levels. It shows 

 no trace of having attempted to fork. That it is the same coral appears likely from the 

 similarity in general character of the calicles. The section has a smaller axial strand, but 

 otherwise agrees. It is in this fragment that we can trace the gradual appearance of the 

 raised wall-ridges, the small nodulated and echinulated septa and the pali together forming 

 a sort of loose open mosaic of granules over the surface. 



a. Adhering to a bivalve, see PI. IX. fig. 3, right hand figure. ) ^^^^ j^ -^ ^544 



b. With coiled worm-tube, see PI. IX. fig. 2, right hand figure. j 



