28 Mr. H. M. Bernard on the 



e. g. the genus HeUolites, developed from a prototlieca which 

 liad fallen over. From Lindstrom's figures* we gatlier that 

 the lip which touched the ground expanded as a flattened 

 epitheca over the substratum, and buds appeared at intervals 

 upon it. Especially ciiaracterislic are the various wrinklings 

 and ridges which appear on the upper face of the epitheca 

 between the buds. As the living layers were periodically de- 

 tached from and rose above this epitheca they secreted tabulate 

 floors, which repeated its wrinkles and foldings. In this way 

 the structure seen in the section typical of the Heliolitidte was 

 produced. Tlirough the tabulate lamina which form the 

 bulk of the coral the calicles run as tubes, while smaller tubes 

 also appear in many cases in the intervening tabulate tissue. 

 These smaller tubes receive their explanation as the continua- 

 tion of the folds or wrinkles already mentioned through the 

 whole series of tabuke. Such folds or wrinkles would run as 

 naturally through a series of tabular as the septa run appa- 

 rently continuously through the tabulas of Montlivaltla, as 

 already explained in fig. 3 and p. 8. 



If, however, we had had no knowledge of the origin of 

 JlelioUtes, we should have assumed that it had been built up 

 of calicles with the form shown in fig. 13./. And, indeed, 

 this is the form which the calicles of the adult colony assume, 

 but it is not arrived at by a symmetrical outward folding of 

 the rim of tlie prototlieca, but indirectly from a parent the 

 unmodified prototlieca of which fell over in the way already 

 described. We owe the small size of the calicle of Ileliolites 

 to this fact. 



The chief difFtrence between the Paleozoic and Hecent 

 astrffiiform corals is due entirely to the more recent development 

 of the radial or septal, as compared with the concentric, proto- 

 thecal foldings. In Palaeozoic times the former were not very 

 pronounced, so that the flattened or curved sides of the proto- ' 

 thecal cups with their tabulate floors formed the most cliarac- 

 teristic portion of the skeleton. The cup was, however, 

 never quite flattened out, there is always the remains of the 

 bend where tiie lip first turned over. These bends frequently 

 form ring-folds (see fig. 13^), which become the walls of the 1 

 fossa3, while tabula? form not only the floors of these fossa3, I 

 but also the areas which intervene between the fossae. These 

 areas are variously sculptured with radial septa, and when 

 the respective areas of the individual calicles are not marked I 

 off from one another, the septa of one may run into the septa ' 



* See K. Sv. Vet.-Akad. Haudl. xxxii. (1899), pi. i. figs. 25-28. Com- 

 pare the case of Pal(soci/clus referred to above. 



