MORPHOLOGY OF THE CORAL SKELETON, 45 



showed distinct lines of growth crossing the trabeculae. in a crenate 

 fashion. 



Crenate margins are due to the projection of the axial portion of the 

 trabecula, but the fibro-crystals terminate along a rounded curve. The 

 curve is sometimes a semicircle, the center being below the, trabecular 



apex. 



It should be noted here that in corals which typically have septa with 

 entire margins, the fusion of the trabecula?. may not always keep pace with 

 their s'rowth, and thus sometimes a trabecula or several trabeculae may pro- 

 duce a dentation composed of one or several trabeculge. Caryoplujllia dalh 

 (PI. IX, fig. 2c) and Parasmilia lucloviciam (PI. IX, fig. 9) are illustrations. 

 Quite often young septa may have dentate margins, while the margins of 

 the older septa may be entire (cf Endopachys). 



Septal dentations are of two kinds. The first is typified by Galaxea or 

 Manicina. Each trabecula ends on the septal margin in a distinct simple 

 tooth. The amount of prolongation of the teeth is variable. In the former 

 genus the teeth are quite short, while in the latter they may be rather long. 

 The second kind forms the coarsely toothed or spined septa. Mussa is prol^a- 

 bly the best illustration. Each compound trabecula forms a large tooth 

 or spine, and each minor component trabecula of the compound trabecula 

 has its minute dentation on the large one. PL I, fig. 4, illustrates the 

 dentation of a septum of Antillia ponderosa (Duncan) from the Bowden 

 beds (Oligocene) of Jamaica. There are large teeth, each of Avhich possesses 

 secondary dentations corresponding to the constituent trabeculse. 



LATERAL ORNAMENTATION OP SEPTA. 



This subject is best introduced by considering the structure of granula- 

 tions. Oo-ilvie has given a thoroughly satisfactory treatment of these. 

 They are fonned by the projection of fiiscicles of filjro-crystals beyond the 

 o-eneral septal surface. A granulation may coiTespond to one or to several 

 combined centers of calcification; in fact, a gi-anulatiou may be derived in 

 part from the calcification centers of several trabecule. 



The arrangement of the granulations on the septal faces corresponds to 

 the courses of the trabecule, but is sometimes due to the fact that a granu- 

 lation is formed from calcification centers belonging to several trabeculse. 

 The trabecular courses may not be easily recognized at first. 



