102 MADREPOKARIA. 



90. Porites West Indies x. 25. (P- Americana incertce sedis quinta et vicesima.) 



(PI. VI. fig. 5.) 



[Coll. Poland ; British Museum.] 



Description. — The corallum is encrusting, and thickens somewhat evenly over the whole 

 surface, so that the centre is but slightly convex, being about 1 '3 cm. thick and 10 cm. long by 

 5 cm. across. It adheres to an old bottle, and is seen under the branching stock in PI. XY . 

 fig. 4. 



The calicles are all flush with the surface and about 2 mm. across, but the outlines are 

 nowhere sharply defined. The walls are remarkable, in that no concentric elements come to 

 the surface, indeed, continuous concentric rings of tissue do not exist. What threads there are, 

 are arranged in sharp, irregular and interrupted zigzags which either interlock or separate 

 adjacent calicles very irregularly (see Table IV. p. 138) ; seen sideways, the surface skeleton 

 consists of low exsert plates and points. The septa are long, very irregular, bent, slightly 

 nodulated and straggling, continuing the confused strands of the walls into the confused colu- 

 mellar tangle, and but for their traces of radial arrangement, the whole surface skeleton would 

 be one continuous, open, but irregular, angular network. Tliis, indeed, it becomes when the 

 surface is abraded ; the calicles are then soon indistinguishable. The order of the fusions of 

 the septa and of the pali is only just traceable, and there is no clearly distinct fossa. 



In the section, the skeletal structure is remarkable. It consists of very open fluent 

 reticulum of which the filaments expand frequently into flakes ; these flakes are wavy, but 

 largely horizontal. Its trabecular or vertical elements seem to rise up wavelike from these 

 flakes. There seem to be very few sharp angles between the vertical and horizontal elements. 



This is the explanate form upon which the branching P. West Indies x. 21, rises, see above, 

 p. 97. 



Unfortunately, there is no information about its locality. It adheres to an old-fashioned 

 bottle. Its surface has been much abraded, but parts of the original are left. There are several 

 growth edges with their epithecal supports visible round the stock, and at times with the 

 wavy flaky texture of the skeleton exposed. The very remarkable, stout, network appearance 

 of the surface skeleton strongly recalls the appearance of some of the Mediterranean fossil 

 Poritids, and suggests that these latter may have belonged to the Atlantic group and not to the 

 Indo-Pacific region.* 



The perfectly superficial character of the calicles apart from the arrangement of the 

 skeleton separates this completely from the astraeoid group, although it is an encrusting form 

 (see Introduction, p. 15). 



a. Zool. Dept. 1903. 7. 31. 1. 



• It is now very widely believed that the fauna of the West Indies was at one time either 

 directly connected with, or very greatly influenced by, that of the Mediterranean area ; cf . Gregory 

 Quart. Journ. G«ol. Soc. li. (1895) p. 255. 



