46 THE VOYAGE OF H.M.S. CHALLENGER. 



the inner surface. Constant as to the thickness of their rays, only near the osculum ex- 

 ceeding 0-002 mm., the gastric quadriradiate spicules vary extremely with regard to the 

 comparative length of the rays, as well as with regard to their form and their angles. The 

 apical rays, which, in the tubar quadriradiates do not exceed the length of the facial rays, 

 and are often still shorter, grow much longer in the gastric quadriradiate spicules, and near 

 the oscular part of the tube attain 0-18 mm. in length, 0-005 mm. in diameter, the corre- 

 sponding facial rays rarely exceeding the length of 0'06 mm., the lateral rays remaining 

 of the same diameter (0-005 mm.), the basal ray growing rather thinner. 



Skeleton of the cortex. — The triradiate and quadriradiate spicules of the cortex are regular, their 

 rays sharp-pointed, more or less stout, the proportion between their length and thickness 

 varying from 6 : 1 to 12 :1. With respect to their dimensions, the quadriradiate are con- 

 nected with the triradiate spicules by intermediate stages ; the length of the rays of the 

 quadriradiate reaching 1 mm., that of the rays of the triradiate not exceeding - 6 mm. 

 These spicules lie apart from the centripetally directed apical ray of the quadriradiate 

 spicules, parallel to the outer surface, but the direction of their basal rays is variable. 



Skeleton of the osculum, — The skeleton of the border of the oscular circle consists exclusively of 

 rectangular sagittal triradiate spicules, marked out by their horn-shaped lateral rays, lying 

 parallel to the line of the border. Their size is extremely inconstant, the length of the 

 rays varying from 0'05 to 0'25 mm., and the proportion between the length and the thick- 

 ness from 10 : 1 to 20 : 1 The comparative length of the basal ray is also variable ; in 

 most cases, however, this ray is shorter and rather thinner than the lateral. 



Colour. — Yellowish-grey. 



Habitat. — Station 36, April 23, 1873, off Bermudas ; depth, 32 fathoms; mud. 

 Station 186, September 8, 1874 ; lat. 10° 30' S., long. 142° 18' E. ; Cape York, Aus- 

 tralia ; depth, 8 fathoms ; coral sand. 



Amphoriscus, Hseckel. 



Syconidse with non-articulated tubar skeleton, the supporting spicules of whose com- 

 paratively thin cortex are either triradiate or quadriradiate, or both triradiate and 

 quadriradiate together. 



Amphoriscus poculum, n. sp. (PI. IV. fig. 4 ; PI. V. figs. 2a-2f). 



The single specimen representing this species in the Challenger collection is of tubular 

 elongated form, 36 mm. long. 4 mm. broad in its middle and superior part ; towards the 

 closed end the tube becomes rather narrower. The individual is bare-mouthed; the 

 outer and inner surfaces are slightly roughened by the cortical and gastric triradiate 

 spicules respectively ; the average thickness of the walls does not exceed 0'6 mm. 



