218 
concinna have a considerably more perforated wall than the original 
part of the corallum from which they have grown out. 
The specimens answering to the diagnosis of F. plana, as given 
by D od er le in, are connected with F. concinna by a gradual series 
of specimens with septal dentations and costal spines of various 
size. I have united as F. concinna all specimens with a solid wall 
and those in which only a few perforations are to be seen in the 
marginal part of the disc, whilst the specimens with a clearly 
perforated theca are recorded under F. repanda. I admit that, in 
doing so, the distinction between these two species is somewhat 
arbitrary, and perhaps the three species F. plana, F. concinna and 
F. repanda had better be united under this latter name, but for 
the present I retain the two species, from each of which 1 have 
some representatives showing the characteristics as given by Db- 
d e r 1 e i n. 
In the literature there are some remarks on the difficulties in 
distinguishing these three species of the repanda-grou'p. As for the 
perforations of the theca, after Vaughan (1907) „F. plana, F. 
concinna and F. repanda form a closely related, or even a contin- 
uous series, with a passage of a solid wall to one that is abundantly 
perforate.“ (p. 126). The occurrence of a number of intermediate 
forms induced Gardiner (1909) to unite F. plana and F. concinna 
as one species F. concinna, from which F. repanda remains separated 
as a distinet species. In a later paper (1918) Vaughan places 
F. plana in the synonymy of F. concinna. Van der Horst (1921) 
also distinguishes only the two species F. concinna and F. repanda 
in the same way as Gardiner and Vaughan. Among the 
material of the Siboga Expedition there are a number of flat spe¬ 
cimens from Stat. 315 with a slightly elevated central part of the 
upper surface belonging to F. concinna. The septa and costae of 
these specimens have exaetly the same structure. In some of them 
the theca is strongly perforated, so that only a small central part 
has a solid wall, whilst in other specimens the theca is altogether 
imperforate (cf. also Van der Horst 1921). 
The greater part of the nine regenerating specimens from the 
reef of Lontor presents no peculiarities of special interest, the pro- 
cess of regeneration takes place in quite the same way as in F. 
repanda (cf. fig. 74). One specimen has become nearly circular 
