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 coucave upper margin, as is shown ia 

 the figure (Plate XIII. fig. 5). 



The quinaries resemble the primaries and secondaries in shape, b»it 

 are of course much smaller ; those quinaries which are adjacent to 

 the primaries and secondaries being much larger and more promi- 

 nent than those adjacent to the tertiaries, and joined to the primaries 

 and secondaries by an upgrowth of the wall. Tlie 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 tliese 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 centims. ; 

 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 I centim, 



III. Comparison q/Stephanotrochus moseleyanus with other Species 

 of the Genus. 



In comparing 6^. moseleyanus with other species of the genus 

 Stephanotrochus, which are four in number, all described by Mose- 

 ley, 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 upgrowtiis, 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 second- 

 ary septa in .S. moseleyanus as there is in S. platypus, diadema, and 

 discoides ; but the primary and secondary sej)taare equal in size, and 

 can only be distinguished by their position with regard to the long 

 axis of the coral, as in S. nobilis. 



On the other hand, 'S'. moseleyanusn^reei best in general shape with 

 -S'. diadema and platypus, and differs from S. nohilis, 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 accom- 

 panying diagrams (p. 131), which illustrate the arrangement of the 

 septa in each species of the genus ; it will be seen that h>. 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. 



