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



be with, or without lateral tubercles at the expanded end. Finally, I should mention 

 that here and there small discohexasters occur with numerous terminal rays on the 

 expanded ends of the principal rays, like the similar structures in RhabdocalyjJtus 

 roeperi, represented in PI. LXV. fig. 4. 



The gastral skeleton consists of strong, rough oxyhexacts, similar to those in the 

 genus BatJiijdorus. 



2. Rliabdocalyptxis rceperi, n. sp. (PI. LXV.). 



To the south of Puerta Buono, in Patagonia (Station 310, lat. 51'' 27' 30" S., long. 

 74° 3' W.), from a depth of 400 fathoms and a blue mud ground, the trawl brought up a 

 cup-shaped Hexactinellid, 16 cm. in length and 9'5 cm. in maximum breadth. The solid 

 inferior portion of the sponge is contracted into a cylindrical stalk, 2 '5 cm. in thickness. 

 This stalk is bent to the side, as if to be attached to some solid body, but the rest has 

 been unfortunately torn away. The somewhat bulging wall of the cup has a thickness 

 of 8 mm. at the lower part, but decreases gradually towards the upper margin, and ends 

 in a simple smooth margin, bent slightly outwards. The sharp, uniform, circular edge 

 exhibits no projecting marginalia. Through the thin even lattice- work of the dermal 

 membrane are seen the irregularly scattered, elongated, angular or spindle-shaped pits, 

 from which roundish canals extend towards the centre. On the inner surface round 

 sharply contoured depressions of various sizes occur, into the bottom of which the more 

 or less wide excurrent canals of the efferent system open (PL LXV. fig. 1). 



Besides this large specimen a small, fiat, wide cup- or basin-like form was obtained at 

 the same locality. It measured 2 cm. in maximum breadth and 1 cm in height, but was 

 also torn away from its connection, and exhibited only a torn base, 1 "5 cm. in breadth. 

 From this the side wall of the body, measuring about 2 mm. in thickness, arises, pro- 

 jecting obliquely upwards and outwards, and continued on to a smooth, circular, sharp- 

 edged mai'gin, measuring 2 cm. in diameter (PL LXV. fig. 2). In perpendicular cross 

 sections through the wall of the cup one can readily detect the alternating afferent and 

 efferent canals, and the folds of the chamber layer which extends between them. 



The main portion of the parenchjrmal skeleton consists of long slender diacts with 

 rough pointed or slightly club-shaped ends, with or without central nodes, like those 

 which have been ah-eady so often described in this family (PI. LXV. fig. 11). There is 

 an isolated occurrence of small, weakly-developed oxyhexacts ^dth fine straight rays 

 (PL LXV. fig. 6), and a greater abundance of oxyhexasters wth short, sometimes very 

 short, principal rays, bearing long, diverging, straight or wavy, fine terminals (PL LXV. 

 fig. 5). The number of terminals on each principal ray varies from two to three, while 

 less frequently only one is present. 



Not unfrequently the principal rays are so short that they can hardly be detected. 



