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Show 130 MR. W. L. SCLATER ON A NEW [Feb. 16, that are so prominent, the edge towards the columella dips down so that the septum has a strongly concave upper margin, as is showu in the figure (Plate XIII. fig. 5). The quinaries resemble the primaries and secondaries in shape, but are of course much smaller; those quinaries which are adjacent to the primaries and secondaries being much larger and more prominent than those adjacent to the tertiaries, and joined to the primaries and secondaries by an upgrowth of the wall. The tertiaries and quaternaries resemble one another, since they both have a straight upper margin, not concave as is that of the primaries, secondaries, and quinaries. All these details with regard to the arrangement of the septa will be best understood by the examination of the drawing (Plate XII. fig. 1), which gives a diagrammatic representation of the septa, tentacles, and mesenteries. All the septa are covered with granules arranged in lines showing the lines of growth. The measurements are as follows:-longer diameter 5 centhns. ; shorter diameter 4^ centims. ; height of the corallum from the base to the tip of the highest septum 2 centims.; height of the edge of the cup 1 centim. III. Comparison o/"Stephanotrochus moseleyanus with other Species of the Genus. In comparing S. moseleyanus with other species of the genus Stephanotrochus, which are four in number, all described by Moseley, from the deep sea, the first point that is noticed is the much greater development of the pali, which in all the other species are merely slight thickenings of the internal ends of the septa, but which in S. moseleyanus form a crown of stout upgrowths, supporting the internal edge of the oval disk. Again, compared with all the other species of the genus, the primary and secondary septa are very much stouter and more exsert, the line between the palus and the other end of the septum is very much more concave (see Plate XII. fig. 5). The septa form five complete cycles, and are remarkable for their regularity; this is also the case in <S. diadema, but not in the other species of the genus. There is no plain distinction of size between the primary and secondary septa in S. moseleyanus as there is in $. platypus, diadema, and discoides ; but the primary and secondary septa are equal in size, and can only be distinguished by their position with regard to the long axis of the coral, as in $. nobilis. On the other hand, S. moseleyanus agrees best in general shape with S. diadema and platypus, and differs from S. nobilis, in which the corallum is deep and cup-shaped, whereas that of S. mosleyanus is flat and saucer-shaped. The differences between the five species are shown by the accompanying diagrams (p. 131), which illustrate the arrangement of the septa in each species of the genus ; it will be seen that £. moseleyanus agrees best with S. platypus in this matter, from which it differs only in having the internal ends of the quaternaries turned in on to the tertiaries, while in S. platypus all the septa are quite straight. |
