208 THE VOYAGE OF II.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 hypoccelus, n. sp. (PI. XIV. figs. 5, G). 



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 sjDecies, excepting that the perforations of the base are larger and 

 more regular in arrangement, and that the trabecules 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 ecpial 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-described 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 

 bifurcate 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 laminae 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, 9 mm. Length of one of the spines, 7 mm. 



Only one specimen was obtained from a great depth. 



Station 299. S.E. Pacific Ocean, off Valparaiso. Lat, 33' 31' S., long. 74° 43' W. 

 2160 fathoms. 



