MORPHOLOGY OP THE CORAL SKELETON. 49 



that they fuse together. The following species illustrate this kind of wall : 

 Manicina areolata (PI. I, fig. 3, part of figure), Eusmilia knorri (PI. II, fig. 

 2), Caryophyllia cornuformis (PL II, fig. 3), Haimesiastrtsa petrosa (PI. XVII, 

 fig. 5), DicJioca'tiia alabamensis (PI. XV, fig. 4b), and others. 



The eutheca of von Heider is formed by new centers of calcification 

 being introduced between the distal ends of the septa to effect fusion. This 

 type of wall is illustrated by Caryophyllia communis (PI. II, fig. 4), and 

 Oculina diffusa (PI. II, fig. 5). 



There has been considerable difference of opinion among various stu- 

 dents of coral morphology as to the systematic value of eutheca and 

 pseudotheca. Therefore I have taken occasion to study the mural consti- 

 tution of a considerable number of genera, to determine, if possible, the 

 amount of importance that should be attached to its structm-e. 



Caryophyllia communis (PI. II, fig. 4) and Caryophyllia cornuformis (PI. II, 

 fig. 3) will show that the character of the wall is not of generic importance 

 unless the genera be separated on that feature alone. I would call special 

 attention to the difference in spacial relations in these two cross sections. 

 In the coral where the septa are remote from one another the theca is a true 

 theca, but where the septa are crowded a pseudotheca is present. Spacial 

 relations seem to be the determining factor. 



PL V, fig. 8, representing a section of Platytrochus stokesi, illustrates 

 another instance of pseudotheca among the Turbiuolida?. This section is 

 described on page 74 of this paper and need not be further noticed here. 



An examination of the walls of several genera placed by Ogilvie in 

 her Amphiastraeidse was made because in defining the family she says 

 "true theca present."^ 



Pectinia mceandrites (Linn.) possesses in some instances undoubted tm.e 

 theca, but in others the theca seems false, formed by the fusion of the distal 

 ends of the septa. Dendrogyra cylindrus Ehr., the type species of the genus, 

 possesses an absolutely typical pseudotheca. The section of Eusmilia knorri 

 M.-Edw. and H., is extremely interesting, because in the same slide there are 

 both true theca and false theca. PL II, fig. 2, is drawn from a place where 

 false theca is present. In other places the true thecal centers of calcifica- 

 tion are perfectly distinct and are arranged in lines perpendicular to the 

 median septal planes. The wall undergoes peripheral secondary thickening, 



'Op. cit.,p.334. 

 MON XXXIX 4: 



