DESCKIPTIONS OF SPECIES. 141 



septa. This is an inference drawn from the distribution of the strise on some 

 of the more clearly exposed pali. 



A thin section parallel to the flat surface of a septum shows very dis- 

 tinctly the trabeculee with the line of divergence. The width of the trabeculse 

 varies from 0.05 to 0.128 mm. They are narrower at the line of divergence, 

 and become wider as they pass away from it. New trabecular are formed by 

 an apparent bifurcation of those having their origin at the Une of divergence. 

 Calcification centers are arranged along the trabecular axes at points from 

 0.04 to 0.06 ram. apart. The fibro-crystals pass upward and outward from 

 the calcification centers, i. e., with reference to the trabecular axes. In the 

 transverse sections of the septa the calcification centers show the same 

 variation in distance apart that the trabecuhij showed in width. A large 

 number were measured, with the following result: 0.024, 0.028, 0.04, 0.048, 

 0.06, and 0.128 mm. As would be expected, the calcification centers are 

 more crowded in the median portion of the larger septa than they are in 

 the costal or that portion near their inner termination. The fibro-crystals 

 pass outward from the median septal plane, toward the interior of corallite, 

 and at a rather small angle except at the inner ends of the septa. A 

 longitudinal tangential section of the septa showed calcification centers 

 ran'o-ed one above another, with fibro-crystals passing upward and outward 

 from the median septal plane. 



Only the cross section of D. alahamcnsis will be compared with the pre- 

 ceding. There is practically no difference in the microscopic characters 

 of the two. Measiu-ements of the distance between calcification centers 

 gave the following: 0.04, 0.048, 0.053, 0.08, and 0.144 mm. The section 

 parallel to the flat septal surface is not satisfactory, and as there is only one 

 specimen in our collection, I shall not have another section cut. The larger 

 septa have thickenings on their inner ends. These in cross sections are 

 elongate elliptical and probably represent pali. 



A few notes on the wall of tliis species may be added. Typically the 

 wall is a pseudotheca, but quite often calcification centers are present 

 between the distal ends of the septa. There can scarcely be any doubt that 

 these centers represent the beginnings of young septa. 



The description of the septal structure given above should be compared 

 with that of Galaxea given by Miss Ogilvie.' 



iMicroBcopic and Systematic Study of Madreporarian Types of Corals, pp. 106-121 ; Korallen 

 der Stramberger Schicbten: Pahi^ontograpbica, Supplement II, Sect. VII, 1S97, pp. 80-83. 



