152 THE VOYAGE OF H.M.S. CHALLENGER 



From seven to nine cribriform organs are present in each interbrachial arc ; they 

 are wide and occupy nearly the whole of the plates, in large examples adjacent organs 

 being confluent in the neighbourhood of the horizontal suture. Their structure is 

 papilliform. (See PI. XXVII. fig. 20.) 



The ambulacral furrows are wide when expanded, occupying the whole of the actinal 

 aspect of the ray, but when contracted are arched over and closed in by the adambulacral 

 armature. The adambulacral plates are elongate and subrhomboid, the margin towards 

 the furrow and the actinal surface being incurved — suggestive of the appearance of a 

 caudal vertebra. The armature of the adambulacral plates along the greater portion 

 of the ray consists of four spines, the aboral spine being the longest ; near the mouth, 

 however, there are five spines, which are short and subequal. The spines are compara- 

 tively short, with a wide robust base, thence they taper, are sharply pointed, and slightly 

 compressed, and all radiate at different angles from the plate. On the plates near the 

 mouth the spines are much shorter, subequal, rapidly pointed, and quite flat. The bases of 

 these spines are united by a more or less continuous membrane. In large specimens a 

 small granule is present behind the furrow series, on the actinal surface of the plate and 

 close to its adoral extremity ; near the mouth even two or three are sometimes found. 



The mouth-plates are large and prominent, with a widely open median suture, the 

 apposed margins of the plates being bent downward with a gentle curve until at right 

 angles to the actinal surface. Their armature consists of a comb of seven or eight short 

 flat spinelets, similar to those on the innermost adambulacral plates, situated on the 

 margin of the plate adjacent to the furrow, and there are one or two more prominent and 

 conical ones at the innermost extremity, which are directed towards the centre of the 

 actinostome. No spinelets or tubercles are normally present on the actinal surface of the 

 mouth-plates, although in the largest specimen four or five granules form a line parallel 

 to the sutural margin. The aboral extremities of the mouth-plates are widely open, and 

 the odontophore is exposed superficially. 



The actinal interradial areas are large and elongate in the direction of the median inter- 

 radial line ; they are paved with squamous intermediate plates, the whole being covered with 

 a thin membrane. The plates are broader than long, imbricate slightly, and are arranged 

 more or less in columns, which latter may however become somewhat irregular as they 

 approach the mouth-angle, consequent on the increase in the size of the plates, which are 

 also more irregular in shape there. A few small granules, very widely and irregularly 

 placed, occur on the plates here and there. 



Colour in alcohol, greyish white, the paxillar area and the cribriform organs having a 

 slightly brownish tinge. 



Locality. — Station 346. Between the south coast of Africa and the Island of Ascen- 

 sion. April 6, 1876. Lat 2° 42' 0" S., long. 14° 41' 0" W. Depth 2350 fathoms. 

 Globigerina ooze. Bottom temperature 34 o- Fahr. ; surface temperature 82 0- 7 Fahr. 



