208 THE VOYAGE OF H.M.S, CHALLENGER. 
Station 157, in the Southern Indian Ocean, in about the latitude of Heard Island, but 
far to the east of it. Lat. 53° 55’ S., long. 108° 35’ E. 1950 fathoms. 
Station 323, South Atlantic Ocean, east of the Rio de la Plata. Lat. 35° 39’ S., 
long. 50° 47° W. 1900 fathoms. 
Leptopenus hypocelus, n. sp. (Pl. XIV. figs. 5, 6). 
The corallum is, as in the last species, discoid, but is concave beneath, and cor- 
respondingly convex above. The corallum is constructed in a closely similar manner to 
that of the preceding species, excepting that the perforations of the base are larger and 
more regular in arrangement, and that the trabecule composing the network between 
them are finer and more delicate. The margin of the disc is circular, with forty-eight 
very short and equal projections placed on it at equal intervals, and corresponding in 
position to the costal trabeculae, of which there are a like number. The septa are much 
higher than in the last-deseribed species. They are in six systems and four cycles, with 
rudiments of a partial fifth system. The primaries are free, whilst the remaining septa 
form deltoid masses. The fork formed by the tertiaries at their junction and union with 
the secondaries is covered in by a large area of curved laminar matter, which is extended 
on to the fork formed by the divergence of the outer quarternaries in each system from 
the tertiaries. The secondaries are continued straight to the margin of the disc, and do 
not branch. The tertiaries bifurcate near the margin of the disc, a small laminate 
expansion being developed at the fork, and the outer quarternaries in each system 
bifureate also slightly somewhat farther out, thus adding septa which may be considered 
as part of a fifth cycle. All the septa bear long spines on their margins. From the 
secondary septa, at the point where they are lapped over by the lamine in the forks 
formed by tertiaries, spring six very long and stout spines, one from each septum, which 
are directed outwards at an angle of about 45° with the horizontal plane of the corallum ; 
beneath these monster spines, which are the only ones borne by the secondaries, these 
septa have smooth and even incurved free margins, which are continued up on to the 
spines beneath, and act as struts and supports to them. All the other septa bear spines, 
but much smaller ones than those of the secondaries, and much more delicate, being long 
and spicular-like, but all directed outwards at about a similar angle. The columella is 
composed of a few similar spicules connected together by lamellar matter. 
Extreme diameter of the corallum, 20 mm. Extreme height from the basal plane to 
the centre of the columella, 5 mm.; to the tip of one of the long spines of the secondary 
septa, 9mm. Leneth of one of the spines, 7 mm. 
Only one specimen was obtained from a great depth. 
Station 299. S.E. Pacifie Ocean, off Valparaiso. Lat. 33° 31’ S., long. 74° 43’ W. 
2160 fathoms. 
