154 THE VOYAGE OF H.M.S. CHALLENGER. 
appears to be adult, and though closely allied to the last species to be distinct from it 
specifically although it was obtained at the same time. 
Diameter of the single specimen, 12 mm. 
Station 120. Off Pernambuco, Brazil. 675 fathoms. 
Stephanotrochus platypus, Moseley (Pl. II. figs. 4, 4a, 4b; 5, 5a). 
Ceratotrochus platypus, Moseley, Proc. Roy. Soc., 1876, p. 554. 
The only two specimens obtained are of a dull opaque white colour, and had evidently 
lain dead on the sea-bottom fora long time. The corallum is circular with a horizontal base, 
from which the low wall rises abruptly and almost vertically. In the larger of the two 
specimens there is no trace of a peduncle, but the remains of a spiral gasteropodous shell 
are to be seen embedded in the coral tissue. In the smaller specimen an indication of a 
peduncle is to be seen arising also from a spiral shell, which is in this instance not deeply 
embedded as in the other. In the larger specimen the base is almost flat, but 
somewhat irregular in surface; in the smaller it is hollowed out around the point of 
attachment ; the cost are simple slight rounded ridges continued from the centre of the 
base to the margin of the calicle, only the primary and secondary are well marked ; there 
are no costal teeth or spines. There are six systems of septa and five cycles; the quinary 
septa are incomplete, and also many of the quaternary ; no lateral fusion of septa occurs; 
the septa are all straight. The primary septa are continued to the very centre of the 
calicle and there meet in a point; the secondary are continued nearly as far, and there is 
no columella properly so called, merely a very small amount of hard tissue present, solder- 
ing the adjacent inner ends of the septa laterally. The primary and secondary septa are 
exsert to an extraordinary degree, rising far above the margin of the calicle, and terminat- 
ing with nearly horizontal edges; the primary septa are considerably higher than the 
secondary. The tertiary and quaternary septa rise only just above the margin of 
the calicle, but the quinary septa next the primaries rise very high and are fused to 
them externally by continuations of the wall; the quinaries next the secondaries are 
also high and similarly fused to these latter but do not rise quite so high as those 
next the primaries. Curved rows of granules are present on the septal faces as in 
Stephanotrochus diadema, marking lines of growth. The free margins of the principal 
septa are much curved, in the smaller specimen bent nearly at a right angle. On these 
margins, in the case of some of the septa of the larger specimen, a slight indication of a 
paliform elevation is visible. ; 
Extreme diameters of the calicles in the two specimens respectively, 46 mm. and 35 
mm. Heights of the walls above the horizontal planes of the bases, 8 mm. and 6 mm. 
Height to the summits of the primary septa, 22 mm. and 19 mm. 
Station 164. Off Sydney, New South Wales. 410 fathoms. 
