208 



10 



The same is true of the exothecal formations. These disappear and the impression 

 left in the chalk is the only clue as to whether the epithecum was present or not. Costa, 

 on the other hand, leave visible traces. 



The matter may be summed up thus; 



The impression determines the outer surface of the theca. 



— — — costae. 



— — — epithecum. 



— form of the coral. 



The stone-kernel determines the number and proportionate size of the septa. 



— presence of dissepiments. 



— central formation in the depth of the coral. 

 Cutting the stone kernel lengthwise determines the upper septal edge. 



— lateral surface of the septa. 



— columella. 



Cutting the stone kernel crosswise determines the conditions of the calyx. 



— the pali. 



— columella. 



IV. Taxonomy. 



In this paper the arrangement adopted by Zittel: Grundzüge der Paléontologie, I. 

 Abth. 4 Udg. 1915, is followed. It must be noted that the determination often rests on a very 

 loose foundation due to the insufficiency of the material. In a few cases certain characteristics 

 are supposed to be present even though the material at hand has been unable to furnish 

 the proof. 



Possibly future collections will modify the determinations made in regard to the 

 position taken by the species here described. 



The chemical condition of the lime skeleton seems to be one of the important points 

 to be observed in systematizing the specimens. In some cases this seems to consist of cal- 

 careous spar, in others of arragonite, as Johnstrup has shown in his paper on the formation 

 of Faxe chalk. One species which seems to have a calcareous spar skeleton is Epilrochus 

 pusillus, found everywhere with its skeleton in a good state of preservation, whereas other 

 corals from the same locahty only appear as stone kernels. The skeleton of this species must 

 therefore be formed of calcareous spar, while the species which have disappeared were of 

 arragonite. 



