Dr. J. W. Gregory — An Egyptian Millcporoid Coral. 339 



Sporadipora. Seliopora. 



Septa No trace. Eudimentary or 



clearly developed. 



Microspores ... .... Cycio- systems. Irregular. 



Intermediate tissue between 



macropores ... ... Spongy. Tubular. 



Canal system ... ... Ramified, extensive. Short and simple. 



This set of characters is not at once decisive as to the affinities 

 of the fossil ; for, according to the two last, it more resembles the 

 Alcyonarians, and, according to the two first, it is nearer to 

 the Hydrozoa. But the two first characters appear to be by far 

 the more impoi'tant. Seliopora, Heliolites, and PoJytremacis have 

 all well-recognizable septa, and there is no cyclic arrangement of the 

 micropores. In the Hydrozoa the absence of mesenteries leads to 

 the complete absence of true septa, although in some cases the 

 elongation of the micropores leads to the macropores being 

 surrounded by radial laminae ; but these " pseudosepta " are external 

 to the zooids, instead of a whole radial series being formed within 

 a single zooid. The apparent compactness of the walls between the 

 cavities in this fossil is probably exaggerated by the secondary 

 changes: thus Fig. le shows that a series of small, dog-tooth like, 

 crystals of calcite spring from the tabulae and the walls. These 

 crystals show that the whole skeletal tissue has been dissolved and 

 redeposited. The definiteness of the walls is, therefore, not 

 necessarily an original character. In fact, the apparently tubular 

 structure of the " coenenchyma " or intermediate tissue is misleading, 

 for closer study (see Fig. le) shows that the skeleton is reticular 

 and not really tubular. The vertical interspaces act as tubes, 

 but these are formed by the growth of the vertical, trabicular pillars, 

 and not by the calcification of a tubular membrane. 



Hence even when compared with recent corals representing 

 the two subclasses of Coelenterata, there seems no doubt that the 

 Egyptian fossil is a Hydrocoralline. And this view is established, 

 almost conclusively, by a comparison with the Paleozoic forms. 

 The general aspect of the fossil, with its massive, encrusting habit, 

 its prominent blunt knobs, and its irregular, perforated surface, is 

 strikingly stromatoporoid. Microscopic study of sections shows that 

 in spite of the absence of the concentric lamination which is such 

 a conspicuous feature in the Stromatoporidas, the essential structure 

 is the same. 



The work of Professor Nicholson ^ has shown that the Stromato- 

 poridse may be divided into two groups, one of which presents 

 points of resemblance to the Hydractinians, while the other reminds 

 us rather of the structures found in the Milleporidee. From the 

 former section, including the Actinostromida3 and the Labechiidae, 

 this fossil differs by the presence of the functional zooidal tubes, 

 a character which also serves to separate it from the Hydractinians. 

 From the Stylasteridte it diifers by its massive habit, by the reticular 

 structure of the coenenchyma, and by the absence of the extensive 



^ H. A. Nicholson, " A. Monograph of the British Stromatoporoids," pt. i (1886), 

 p. 71. 



