158 THE VOYAGE OF H.M.S. CHALLENGER. 



good deal more prominent than the others. The lateral costse are developed in the lower 

 region of the corallum into aliform projections, which vary much in their width. In the 

 specimen figured they are less developed than in any of the others procured ; they are 

 usually broader towards the base of the corallum. In some specimens their edges are 

 more or less notched ; their surfaces are covered by a series of ridges like those formed 

 by the costae near the apex of the corallum. The ridges are directed at right angles to 

 the line of slope of the coral cup, and are parallel, but here and there irregular ; in some 

 places the costal ridges, where they abut on the lines of origin of the alae, are seen to be 

 bent outwards to join the ridges on them. The outline of the calicle is oval, the fossa 

 is extremely deep, and the whole interior of the calicle open and hollow to the apex, not 

 being filled up by any outgrowths of the septa or columella. The septa are all perfectly 

 straight, with smooth surfaces dotted over with very minute rounded granules and 

 showing curved accretion lines. The primary and secondary septa are equal. All the 

 septa are exsert, the tertiary and quaternary according to their order. There are four 

 cycles of septa and twelve primary and secondary septa, and evidently there must be in 

 the young coral primarily six systems, but in all four specimens the two pairs of lateral 

 chambers at the ends of the long axes of the calicles have developed two additional septa, 

 a tertiary and a quarternary in each, so that there are four additional imperfect systems 

 in each coral, which correspond exactly in all the specimens (see fig. 8a). 



The columella is elongate in form, and remarkably slender and prominent, composed 

 of four or five small columns of roughened calcareous matter partially fused together 

 laterally. It projects up free from the bottom of the fossa formed by the excavated 

 edges of the primary and secondary costaa for a height of 5 mm. At the bottom of the 

 fossa these septa fuse with its base, and it is directly continued below as a narrow lamina 

 perpendicular to the apex of the corallum, being free from any of the additional irregular 

 ealcareous outgrowth which is usually developed about the base of the columella and the 

 inner ends of the septa in many other corals. 



After comparing this coral with specimens of Sphenotrochus crispus, I conclude that 

 it must necessarily be placed in the same genus. It differs from the other Sphenotrochi 

 in the considerable exsertness of the septa, and in having four cycles of septa instead of 

 three, also in the great depth of the fossa ; but these differences are probably due to the 

 large size of this recent species, in all essential particulars it is closely allied to 

 Sphenotrochus crisjius. That species differs from it mainly in its smaller size, in having 

 its costse much larger in proportion, in having its septa denticulate, and in possessing 

 a much shallower fossa ; in the peculiar form of its columella it closely corresponds with 

 Sphenotrochus rubescens. Sphenotrochus auritus (Pourtales 1 ) has a flat protuberance on 

 either side of the base, but these flat expansions are very different from the aliform 

 appendages of the present species. 



1 Hassler Expedition, loc. cit., p. 37. 



