159 



by large, open cancelli through which no tracé of ovicell can be seen. It is not impossible that 

 colonies of this type have developed male sexual organs only, though I have no evidence on 

 this subject. The majority of the colonies are, however, fertile. 



The marginal lamina is generally broad : — an indication of the fact that growth is not 

 complete. In some instances, as in certain specimens growing on shells, it is closely adnate to 

 its substratum. An incidental advantage of this arrangement is well seen on slide 568. B. 1 , where 

 a colony is growing over an area occupied by an encrusting Cheilostome. lts marginal lamina 

 has overspread the Cheilostome, occluding its orifices, and thus removing the competition of 

 what might have been an inconveniently near neighbour. In one or two cases, however, the 

 marginal lamina and some of the peripheral zooecia have been covered by an encrusting 

 calcareous Alga. 



In many other instances the marginal lamina has become completely free from the 

 substratum ; and it may then grow into the saucer-shaped edge which is also found in other 

 species of the genus. 



The cancelli are occupied; — or at least some of them in each colony; - - by the well 

 knovvn radiating, pin-like spines, as shown in fig. 7. Examined with a sufficiently high power, the 

 head of the pin is found to be minutely denticulated, or aster-like. In many cases the cancelli 

 remain widely open ; but in others a cryptocyst-like calcareous lamina develops in an iris-like 

 way at a level slightly lower than the edges of the cancellus. The orifice of the cancellus may 

 be reduced in this manner to a very small opening; and colonies in which this process has 

 taken place may at first sight look very different from those with open cancelli. But even in 

 these cases the cancelli may be seen to have the normal size, since their original edges still 

 project as slight ridges above the level of the iris-like cryptocyst. In some of the specimens 

 from Japan (5. AN) the ridges separating the cancelli are specially high and may be produced 

 into spinous projections at their nodal points (where the walls of several adjacent cancelli unite). 

 In some of these specimens the marginal side of the orifices may be produced into a sharp 

 point ; while in some of those from New Zealand the central side of the orifices may be prolonged 

 into one or two points, in addition to that on the marginal side. These specimens, from Japan 

 and New Zealand, are so similar to the 'Siboga' specimens in the characters of the ovicells 

 that their reference to the same species seems fairly certain. 



Some of the 'Siboga' specimens show distinct indications of regeneration of the entire 

 colony : - - a process which is known to occur in other species of the genus 1 ). This is specially 

 well seen in some large colonies (as much as 8.5 mm. in diameter) mounted on slide 568. B\ 

 In one or two of these colonies, a smaller disc has developed from a part of a larger zoarium ; 

 and the regenerated clisc is produced from one side of the older part of the colony in such a 

 way that it is not in the least concentric with it, but leaves part of the old surface exposed, 

 while the remainder is covered by the regenerated, excentric disc. 



The specimen 251. M. is very doubtfully referred to the present species. Its rays are rather 

 more biserial than usual, and more nearly approach the centre of the colony. The characters 



1) Cf. Pergens, E., 1890, "Rev. Bry. Crét. figurés par D'Orbigny", Buil. Soc. Beige Géol. III, p. 319. 



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