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Show 1883.] MADREPORAR1AN GENUS PHYMASTRAEA. 411 There is considerable distance between the corallites at the surface, amounting to 1 millim. and more, and this is crossed by the junction-processes. These are very variable in their size and distribution ; some do not reach across, and others are constricted in the middle. Very broad ones are exceptional. The irregular shape of the corallites and calices is due to pressure during growth and the pushing upwards of growing buds ; and this irregularity of outline appears to have interfered with the septal distribution. In a very small calice belonging to a small bud, which is nearly symmetrical and circular in outline, there are six primaries; but where a little pressure has produced flattening, one of the primaries is smaller than the others and might be mistaken for a secondary septum. There are six systems of septa in the bud, and in four there is a secondary septum ; two of them are long and two short. In the other two systems, near the flat part, there are no secondaries. A second bud, which is oval elliptical in outline, being compressed from side to side, has six primaries, and where the pressure was at one end the primary there is small. There are, as usual, six systems. In the first, commencing to the right of a primary in the long axis of the calice, there is a secondary which is long, and in the second the secondary is a mere rudiment. In the third system the secondary is rudimentary, and so it is in the fourth ; so that the third and fourth systems, with the intermediate small primary, look like one system. The fifth system has a long secondary and a tertiary, small and rudimentary, on either side ; and the sixth system is like the second. In the larger calices the secondaries equal the primaries, and some tertiaries do tbe same ; moreover, in the same system a tertiary may abort or he rudimentary, so that there are three successive septa equal in length, i. e. a primary, a tertiary, and the secondary, and then comes a small tertiary. In the same calice in the next system, the normal long secondary has short tertiaries on either side ; but the next svstem has a secondary equal in length to the primaries ; on one side of it is a small tertiary, and on the other a long tertiary with a small septum between it and the secondary. This is a very irregular and abnormal distribution. In the next system the secondary is small and the tertiaries are as large as primaries, and between the primaries and the tertiaries is a rudimentary septum. None are found on either side of this secondary septum. The irregularity of the septal distribution in the last system of all transcends any thing I have ever seen. The secondary and the two tertiaries are equal in size and resemble primaries; and there is along septum occupying the position of the fifth order between each tertiary and the secondary. Between one primary and the tertiary there is a septum of the fourth order, and between the other primary (the first in the calice) and the tertiary there are two septa! In tbe largest calices the septal arrangement appears to be without definite arrangement in cycles and systems, and large and much smaller septa alternate. |
