38 EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



Very few observations on this point are known to me, and I have had no 

 opportunity to make any myself. Ogilvie' considered the tliick extrathecal 

 deposit hxid down by many Turbinolids as epithecal in nature. The septa 

 and wall in many corals are externally increased in size and thickness from 

 the outside by the activities of the protruding soft parts. An example is 

 JEusmilia knoni, and the render is also referred to the description and figure 

 of Paracyatluis alternatus, page 105, PI. VIII, figs. 11 and 14, and of Cary- 

 ophylUa daUl, i)age 110, PI. IX, fig. 2. If the definition of epitheca given by 

 Ogilvie is to be retained, it seems to me very doubtful whether such nn 

 external deposit as that described for these species can be considered epitheca. 

 This question will be alluded to again in discussing types of walls.'^ 



PI. I, fig. 2, shows how the epitheca of Mauicina is laid down on the 2iro- 

 jecting outer ends of the septal trabecule. The microscopic structure is 

 quite diiferent from that of the septa and wall, but resembles that of the 

 dissepiments. The minute calcareous fibers do not show a definite grouping 

 around certain clearly recognizable points, centers of calcification, but are 

 placed normal to the epithecal surface. 



SEPTA. 



The basal plaie was descriVjed first, because it is the first part of tlie 

 skeleton formed, and the epitheca next, because it is considered the morplio- 

 . logic continuation of tlie former. After the basal plate, the septa are the 

 skeletal structures next formed. 



In order to introduce the discussion of the septal structure, the septa 

 of Maniciiia areolata (Linn.) will be described in considerable detail. 



STRUCTURE OF THE SEPTUM OF MANICINA AREOLATA (LINN.). 



Exainined macroscopically, witli the aid <>f a hand len.s, tlie septum 

 exhibits on the lateral face a large number of elevated striae that run from the 

 wall to the se[)tal margin. Tlie strire on the inside of the wall pass upward 

 and inward, i. e., the inclination from the perpendicular is towai'd the inside 

 of the calice; on the outside of the wall the stria? at first pass upward, 

 bending outward, but soon come into an almost horizontal position. This 

 Hue, away from which the stride diverge, is called the area or line of diver- 



'Op.cit., p.2.50. 



= Bernard, in the paper already alluded to (pp. 504, ,")05), has ^iven an accurate and detailed 

 account of the epitheca. His statements are in accord with the conclusions of von Koch. 



