42 EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



There is every stage Ijetween this condition and one in which the 

 trabeculai pass horizontally niward (cf. Platycojuia, p. 150 and PI. XVII, 

 fig". 9a, of this paper). Miss Ogihne describes a similar one for Turbinaria 

 (see op. cit., pp. z03-211). Still other instances might be cited, but these 

 serve as examples. 



WIDTH OF THE TKABECUL^. 



The trabecuhie of different corals are of varying widths. In the 

 same septum the trabeculse are narrower at the point of their origin, and 

 become wider as they increase in length. The width of the trabecule is 

 extremely important, because it is one of the factors that determines the 

 character of the septal margin. The smallest that I have measured are 

 those of Haimesiastrcea conferta, which have a width of 0.016 nnn., and 

 those of Eusmilia knorri, which have a width of 0.048 to 0.069 mm. (PI. I, 

 fig. fi). Ogilvie says that the trabeculse of Goniastrnea "so far as they 

 can be clearly distinguished, have a diameter of 0.03 mm. to 0.04 mm." 

 "At the same time the surface ridge has a diameter of about 0.15 mm."^ 



The diameter of the trabeculse in Manicina has already been stated to 

 be from 0.14 mm. to 0.374 mm. A single trabecula in AntUUa: ponderosa 

 (Duncan), from Bowden, Jamaica, may measure 0.83 mm. in diameter; 

 0.55 mm. is not at all large for one. (See PI. I, fig. 4.) 



INFLUENCE OP WIDTH OF TRABECULSE ON THE DIRECTION OP THE CALCAREOUS 



FIBRO-ORYSTALS. 



Ogilvie has frequently stated that in such corals as Euphyllia the 

 fibro-crystals stand almost perpendicular to the median septal plane.^ She 

 does not seem to have studied Euphyllia, herself, but refers to Bourne's paper 

 On the Anatomy of Mussa and Euphyllia and the Morphology of the 

 Madreporarian Skeleton.^ I have not studied Euphyllia, but have studied 

 Eusmilia. PI. I, fig. 5a, shows how tlie fibro-crystals converge downward 

 along the axis of a trabecula. The cross section (PI. II, fig. 2) shows the 

 fibers with an arrangement more or less perpendicular to the median septal 

 plane. There also seems to be a plane center of calcification — i. e., calcifi- 

 cation along a plane. The latter is merely an appearance. In the cross 

 section the trabecular axes can be distinguished as in Manicina, though not 

 so easily. They measure about the same distance across in Ijotli the radial 



1 Ogilvie, op. cit., pp. 148, 149. - Op. cit., pp. 160, 161. ^ Quart. Jour. Microsc. Sci., Aug., 1897. 



