28 Mr. II. M. Bernard on the 



e. cj. the genus HeHoUtes, developed from a prototlieca which 

 had fallen over. From Lindstrom's figures * we gather that 

 the lip which touched the ground expanded as a flattened 

 epitheca over the substratum, and buds appeared at intervals 

 upon it. Especially characteristic 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 Heliolitida3 was 

 produced. Through the tabulate laminse 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 tabulae. Such folds or wrinkles would run as 

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

 rently continuously through the tabulae of Montlivaltia, as 

 already explained in fig. 3 and p. 8. 



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

 Ueh'oh'tes, 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 the 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 caliele of Jleliolites 

 to this fact. 



The chief difference between the Palaeozoic and Recent 

 astrauform corals is due entirely to the more recent development 

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

 thccal loldings. Jn Palaeozoic times the former were not very 

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

 thecal eups with their tabulate floors formed the most charac- 

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

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

 bend where the lip first turned over. These bends frequently 

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

 fossae, while tabulae form not only the floors of these fossae, 

 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 

 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 Paleeocyclus referred to above. 



