24 THE FOSSIL COEALS AND 



guish the species from any member of the genus Isastrcea at once. In some speci- 

 mens the calices are deeper than in others, and the margins of the calices are unequally 

 elevated, whilst the whole surface is gibbous here and there. The sameness of size of 

 the calices in the same specimen is sometimes striking. 



The young forms have a flat base ; and this appears to grow more or less dome- 

 shaped with increasing lateral dimension, and probably the original calice started with 

 a minute peduncle and epitheca. Growth appears to take place by budding just on 

 the outer margin of the calices ; and no upward development occurs, there being but 

 one row of calices in vertical measurement. 



In some of the fossils the base has become covered with a mud containing fossils, and 

 then the specimen appears to be an incrusting form ; but with a little care the epitheca 

 can be distinguished. It is this basal epitheca that gives the species its especial character ; 

 and it is a remarkable fact that Jules Haime should have noticed an epitheca only in 

 an Upper Cretaceous species from Maestricht *. None of the Tertiary forms have it. 



The weathering of the surface brings out the perforate condition of the walls and 

 septa ; and some forms of fossilization, especially an infiltration with calcite, by filling 

 up the interstices, render the form like an Isastrcea with a small columella. When 

 destruction of the original coral has taken place, only portions of it being left here and 

 there, the cast that remains has, of course, no evidence of the former presence of the 

 wall between the calices, and the aspect given is that of an Heliastrsean. It is neces- 

 sary to remember this ; for some specimens from Barki nala might be relegated to 

 another genus than Litharcea. 



LiTHAE^A EPiTHECATA, noUs, var. HEMisPH^KicA. Plate II, Fig. 10, 



The basal surface is concave, and the upper surface is almost hemispherical. 

 The calices are shallow, and hence there must be a vertical successional growth. 



Breadth of corallum I^-q- inch ; height centrally ^ inch. 



Locality. Barki nala. Survey-number G xrf- 



When the fossilization has destroyed the walls, the remarks already made hold 

 good ; but towards the edges some smaller calices show all the specific characters. 



Illustrations of the Species in Plate II. 



Fig. 1. The upper surface of the type of Litharcea epithecata. 



2. The basal epitheca. 



3. A smaller and younger specimen ; calicular surface. 



4. The basal surface. 



5. The basal epitheca of a very small specimen. 



6. Calices of a weathered specimen : natural size. 



7. The calices : magnified. 



8. The structure of the wall, septa, and endotheca : magnified. 



9. A portion of the basal epitheca : magnified. 

 10. View of the variety hemisphcerica. 



* L. Goldfussi, M. Ed. & J. H., Hist. Nat. des Corall. iii, p. 189. 



