15i PROF. p. M. DUNCAN ON THE 



neighbourhood of the outer part of the corallum, especially, it 

 may be discontinuous, several knobs being in a line and sepa- 

 rated by the plain face of the septum. The direction of the 

 curvatures is always with the concavity iuAvards and never out- 

 wards. The breadth of some intersynapticular spaces is greater 

 tban others. 



There are some interesting modifications of the growth of the 

 synapticula. First, these ridges are seen on the faces of some 

 large septa, where the usual thin small septum in natural suc- 

 cession is partly or wholly absent. The synapticula there are of 

 the usual size, are slightly nipped in and then expanded, and ihe 

 free edge of the expansion, or that part which should have been 

 in contact with, a small septum, is a plane surface. Secondly, 

 near the margin of the corallum the outermost synapticula close 

 to the basal wall are in the form of irregular, broad, and high 

 nodules, a small nodule being here and there. 



The first condition indicates that the synapticulum is a growth 

 which may be independent of origin of two opposed septa ; and 

 the second explains the continuation of the basal wall by the 

 union of the irregular nodular and wide synapticula and their 

 subsequent radial growth. It is evident that a tbin septum may 

 grow up and find synapticula ready for it to impinge upon and join, 

 and that the perforations in the basal wall which usually fill uj) 

 with age are openings between basal synapticula which enter, 

 however, interseptal loculi. The union of the adjoining septa by 

 the synapticula causes the lower parts of the interseptal loculi to 

 be filled with a series of canals opening above, and a few opening 

 below, as in Fungia ; but here and there the canals are not per- 

 fect, and run one into the other laterally, or rather in an axial or 

 circumferential direction. 



Some of the most important points regarding tbe synapticula of 

 Serpolitha are their curvature in relation to different septa, their 

 comparative shortness, and occasional interruption and represen- 

 tation by lines of separate growths. It is interesting to note that 

 these lines are not on or along those of ornamentation. There 

 are no dissepiments in Herpolitha. 



"Where the so-called calices are seen on either side of the cen- 

 tral axial series, a condition of the free upper margin of some of 

 their larger septa exists which is remarkable. A separation of 

 the septum appears to be in process, or rather two septa are 

 forming from the old one as their base ; and they are united by 



