52 EOCENE AMD LOWER OLIGOGENE GOKAL FAUNAS. 



between the deposits formed at this angle and that laid down by the broad 

 inner surface of the edge zone. 



The relations of the soft parts of the Turbinolida; to the skeletal parts 

 needs lnl^ch more study, and until such studies have been made we can not 

 know the homologies of all the skeletal structures of the group. In fossil 

 species soft parts can not be observed, but comparisons can be made with 

 recent corals. Sucli a comparative study leads me to the belief, above stated, 

 that the extrathecal thickening of many Turbinolid corals is formed in the 

 same way as in Eusmilia, by the inner face of the edge zone applied against 

 the outside of the corallum wall and peripheral ends of the septa, and is not 

 epitheca according to the accepted definition of the latter. The fact that dis- 

 sepiments ^ sometimes aid in the formation of the corallite wall, or assist in 

 giving it strength, has been noticed by several authors. ~ The wall of a 

 West Indian Lithophyllia (i. Jacera or cubensis, I am not decided about the 

 relations and synonymy of these two so-called species) is strengthened by 

 dissepiments. The relations of dissepiments to the wall of Stephanocoenia 

 intersepta are described on page 153. 



]\Iany corals may have perforate walls, because the septa may not be 

 uniformly thickened throughout their length in tlie thecal ring, or the fusion 

 of the septa may not be effected by the introduction of the so-called true 

 thecal calcification centers. In some Turbinolids, e. g\, genus Turbinolia, 

 there are regular rows of pores between the costal Pores occur also in 

 Trematotrochus, and there are intercostal dimples in iit least some species 

 of Sphenotrochus (cf SpJtcnotrochns nanus, p. 84). Tlic intercostal pores 

 may not be regular, l)ut only occasional, as is noticed in I'aracyathus hellus, 

 page 108. Such occasional perforations may occur in almost any normally 

 impei'forate wall, and have no special significance ; it is only when they 

 occur constantly that they are of systematic importance. 



The walls of such corals as Alveopora belong in the last class. Bernard 

 has described the structure of this genus with great care.'' The wall is 

 formed by the fusion of interlocking septal spines. 



' For discussion of dissepiments, see p. 53 of this paper. 



^ Ogilvie, op. olt., p. 251 ; liernard, On the attiuities of tlie Madreporariau semis Alveopora witli 

 the Paleozoic Favositicbu: Jour. Ijiiin. Soc, London, Zool., Vol. XXVI, 18'JS, p. 500. 

 'Loc. sup. cit., pp. 499-500. 



