SOLITARY CORALS. 211 



3 minims. The six primary sepia are much larger than the others, considerably 

 thickened at their thecal ends, and they, and the two septa adjacent to them, are 

 exsert, forming a crown of six prominent points round the edge of the calice. The 

 edges of the primary septa slope rather steeply inwards and then descend vertically 

 into the depth of the fossa without joining the columella ;. the inner half of the 

 surface of each primary septum is nearly smooth, the outer half hears a number of 

 spinose granules. There are five septa of lower orders in five of the systems and 

 seven in the sixth system (adjoining one of the directive septa), those adjacent to the 

 primary septa being the largest and most exsert ; the smaller septa join the columella 

 very deep down in the fossa. Costa? of the six primary septa larger and more 

 prominent than the rest, forming ridges extending nearly half-way down the corallum ; 

 the remaining costse subequal, extending to the base, the perforations between the 

 costse numerous and relatively large. Columella oval, very prominent, spongy in 

 texture. Buds are formed on opposite sides a little way below the margin of the 

 calice, each bud being astride of a primary costa. 



A single specimen from dee]) water off Galle. 



I have founded this species to receive a small and remarkably beautiful coral, 

 which resembles B. rediviva, Moseley, in the costse and arrangement of the septa, 

 but differs from it in size, in colour (B. rediviva is " reddish coloured," B. taprobance 

 a brilliant white), and in the fact that the secondary septa are not exsert. These 

 differences can hardly be due to immaturity, as the specimen of B. taprobanm bears 

 two fairly advanced lateral buds. 



The septal characters are particularly interesting as being wholly unintelligible 

 unless interpreted in the light of Pourtales' and Duerden's work. In fig. 9a it is 

 evident that, in the lateral system on the left hand of the drawing, the inner ends of 

 the septa marked X. 2 , X. 3 , are the bifurcated arms of the exoccelic septa of the cycle 

 second in order of appearance ; these arms unite together and with the columella 

 very low down in the calice. The septum marked En. 2 is clearly the entocoelic 

 septum of the cycle third in order of appearance. In the upper half of the system 

 the exoccelic septum has bifurcated to form the secondary exoccelic septa A". 3 , X. 3 , 

 and a new entocoelic septum En. 3 is formed in the bifurcation. A precisely similar 

 arrangement obtains in four of the remaining systems, and in each it is the upper 

 member of the exoccelic septa that has bifurcated, giving a dorsiventral arrangement 

 entirely consistent with Duerden's description of the septal succession in Siderastrcea 

 radians. In the left-hand lower terminal system both exocuelic members have 

 bifurcated and an entocoelic septum is present within each bifurcation. In B. rediviva 

 all the systems are similar to this single system in B. ta/probanm, and the arrange- 

 ment would obviously be that which is normal in the Eupsammiidse, if it were not for 

 the preponderant size of the apparent quaternaries, whose outer ends become more 

 or less intimately united to the primary septa. The condition in B. taprobanm is a 

 step towards the septal arrangement in B. verrucaria, Pallas, and B. corrni, 



2 e 2 



