of the IliKjosa to the liriiu/ Zoanlheic. 



3l»5 



/ s 



Fro. 11. 



Diagrammatic representation of the ridges and grooves on the ealii-iual 

 wall, as seen from btdow. Tlie upper border of the fifjuro corre- 

 sponds with the convex side of the coral and the lower with tho 

 concave. The apex is represented as a circular area, instead of as a 

 point, in order to better indicate the twelve primary ridges and 

 grooves, which extend thus far. On each side of the upper half the 

 secondary septa (A, B, C, D) appear as radiating from the alar 

 septum (S), the oldest lying next the primary septum adjacent to 

 the main septum (11); on each side of the lower half the septa 

 (A, B, C) radiate from the counter septum (G), the oldest lying 

 next the alar septum. 



Comparing the schematic Hj^ure with that of Streptelnsma given 

 by Kunth (1869, p. 647) and copied into most of the text-books on 

 palaeontology, it will be seen that the positions at which the septa 

 are added in LophaplujUum are the reverse of those in Streptelasma, 

 In the latter genus, as appears to be also the case in most Zaphren- 

 toids, the new sejUa in the main quadrant are added immediately on 

 each side of the main septum, the oldest being ne.xt the alar septa ; 

 while in the counter quadrants they are added immediately adjacent 

 to the alar septa, the oldest being next the counter septum. 



