158 THE VOYAGE OF H.M.S. CHALLENGER. 
good deal more prominent than the others. The lateral costae 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 costee 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 ale, 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. 87). 
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 costee for a height of 5mm. 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 
calcareous 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, | 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 crispus. That species differs from it mainly in its smaller size, in having 
its costee 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 (Pourtalés') 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. 
Hassler Expedition, loc. cit., p. 37. 
