COLLECTED BY DK WILLEY. 123 



examining the figure with a lens that wherever there are ridges or other irregularities 

 in the surface the gastropores are so crowded that the cycles become quite indistinct. 

 Forskal says that the pores of this species are " minute." Actual measurements of 

 twenty gastropores situated in the middle parts of the corallum give an average 

 diameter of 28 mm. This average is above the average size of the diameters of 

 gastropores in other specimens of Millepora (see list of average diameters of gastro- 

 pores given in my paper in Proc. Zool. Soc), and consequently it would be erroneous 

 to state that in these specimens the pores are " minute." 



The base from which the specimens of this facies spring is, in all cases which 

 I have examined, either narrow or small. The base which supports the whole of 

 the corallum shown in Fig. 1 is only 30 mm. by 10 mm. This is a point of some 

 importance because the character of the ground on which the Millepore embryo 

 settles must to a considerable extent determine its facies. It is quite certain that 

 an embryo settling on a base only 300 square millimetres in area could never give 

 rise to great plates of corallum similar to the one shown in the photograph Fig. 7. 

 The colour of most of the specimens included in this facies is pale yellow brown. 



Facies complanata. 



Several specific names have been given to Millepores which assume the form of 

 a broad leaf or a series of lamellae more or less coalescent. The descriptions given 

 in the literature of the so-called species and of specimens attributed to species are so 

 bewildering that it has become quite impossible to distinguish what form of growth 

 is to be attributed to M. complanata Lunik., M. plicata Esp., M. platyphylla Ehr., 

 and M. foliuta, etc. 



It will be convenient to consider those Millepores which form by coalescence 

 broad lamellae under the name 'complanata.' These forms are practically those 

 included by Pallas in his variety 7, with the following definition: 



" Elegantissima omnium varietas quae effingitur in laminas latas, crassiusculas 

 longitudinalibus plicis undulatis, sublaciniosas margine terminali retiusculo. Hae laminae 

 in rupibus passim congestae, plerumque subparallelo positu ; interdum tamen situ 

 variantes imo decussautes aliquae reperiuntur." 



The photographs given in Figs. 2 and 3 are the two halves of one specimen 

 which shows admirably the manner in which the Millepores of this facies are formed. 



The specimen began life on a broad frond of dead coral 14 centimetres broad 

 and about one centimetre thick at the margin. (In this case the dead coral which 

 forms the support is a Millepore covered by encrusting algae, foraminifera, zoantharian 

 corals, etc.) At first the young Millepore spread as a thin crust over the support 

 forming a broad base. At the same time a certain number of broad digitiform 

 processes grew out from the middle of the base, which became broader and began 

 to coalesce. If the process had been continued a little further, the lines of the 

 original processes would have been obscured and a plate similar to that shown in 

 Fig. 4 would have been formed. 



The specimen shown in Figs. 2 and 3 is only one of several in Dr Willey's 

 collection which give us information as to the mode of origin of the Millepore 



17—2 



