44 EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



this way, they may exist near the septal margin, but as the coi'al increases 

 in ag-e they may be completely closed by further growth of the skeletal 

 elements.' 



Tliere are instances in which septal pores are produced by the discon- 

 tinuity of the trabeculse. Miss Ogilvie^ says: "The irregular shape of the 

 septal pores in Eupsammia is due to the fact that the growth parts of one 

 trabecula may be disconnected, and also the growth parts of adjacent 

 trabeculo:?." Attention is called to the same condition in Balauophyllia and 

 Endopachys described on pages 163 and 189, respectively, of this paper. 



SEPTAL MARGINS. 



The usual descriptive terms applied to the margins of septa are 

 smooth or entire, finely dentate, coarsely dentate, spinose, etc. The char- 

 acter of the jnargins may be traced to two causes. Oiie is the trabecular 

 structure of the septum, and the second is the mode of trabecular growth. 

 The general statement may be made that a septal dentation is due to a tra- 

 becular axis projecting beyond the curve that limits complete trabecular 

 fusion. 



Septa with so-called entire margins may be divided into three classes. 

 The first are those with septa composed of trabecular, that are formed 

 parallel to the septal margin. Platycoenia (see p. 150) has the trabeculas 

 directed horizontals^ inward; therefore the upper septal margin is smooth, 

 but the inner margin is dentate. The second type of entii'e margin is illus- 

 trated by Flabellum. The septum is composed of ascending trabeculse, 

 Imt the axis of the trabecula grows no more rapidly than tlie nonaxial 

 portion, and the resultant form of margin is a continuous curve. Occa- 

 sionally, in Flabellum or Trochocyathus, a trabecular axis may project 

 slightly and form a crenation. Tlie crenate margins will be discussed later. 

 The third type of smooth margin may be illustrated by Eusmilia. The 

 trabecular constitution of the septum has already been descril^ed. The 

 smooth margin in this instance is due to the extremely minute size of 

 the trabecuki?. Pectinia and probably Haimesiastmea are other instances. 

 The septa of 1\ ni(Bandritcs reall}" have very minutely crenate margins. 

 An examination of a thin section parallel to the flat surface of a septum 



'Koby, Mou. polyp, jurass. de la Suisse: M^m. Soc pal. Suisse, Vol. XVI, ]i. .557. 

 = 0p. cit.,p. 19G. 



