HYALONEMA (PRIONEMA) FIMBRIATUM. 295 



thick. The fragment from Station 4742 is a porous lamellar mass 30 mm. long. 

 The two fragments from Station 4740 are also porous lamellar masses, and 30 

 and 35 mm. long respectively. 



The colour of all the specimens in spirit is very light brown. 



The skeleton. The dermal and gastral surfaces are covered by a dense 

 pinule-fur. The dermal and gastral pinules appear to be quite similar. The 

 lateral rays of these pinules, the lateral rays of large pentactines, and rhabds 

 are found in the superficial membranes. The radial, inwardly directed apical 

 (proximal) rays of the pentactines and radially or obliquely disposed rhabds 

 traverse the space underlying the superficial membrane. In the lower part of 

 this region, and in the distal zone of the choanosome, fimbriate amphidiscs are 

 met in large numbers. In some parts of this region these spicules form dense 

 masses (Plate 60, fig. 24). In the walls of many of the internal canals large 

 canalar pinules form a fur, often quite dense. Besides these spicules there 

 occur in the choanosome rhabds, often forming bundles, hexactine megascleres of 

 various sizes, microhexactines, micropentactines, macraniphidiscs, and micram- 

 phidiscs. The micramphidiscs are not numerous and occur chiefly in the canal- 

 walls. In the basal protuberance, from which, in life, the stalk arose, the 

 following spicules occur besides those of the choanosome : — numerous slender- 

 rayed, long-spined tetr- to hexactine acanthophores ; a few monactine-derivates 

 of these ; numerous di- to pentactine acanthophores with stout rays ; numerous 

 more slender, modified, sometimes very strongly curved acanthophore rhabds; 

 and numerous anchor-spicules. 



Besides these spicules which are doubtlessly proper to the sponge, various 

 others, which I take to be foreign, are found, sometimes in large numbers. 

 These are: — pentactines with a very stout, spindle-shaped proximal ray some- 

 times 100 M thick; large amphidiscs of various kinds, most of which are similar 

 to, and probably identical with, the large macrampliidiscs of Hyalonema agassizi; 

 giant pentactine pinules as much as 1.2 mm. long; and other kinds of pinules. 

 The large foreign amphidiscs usually occur in clusters. 



The superficial {dermal and gastral) pinules (Plate 62, figs. 1-4, 16-18) are 

 always pentactine. They have a straight distal ray 63-87 ju long, on an average 

 (of 27 measurements) 71.8 /j, and 3.2-4.8 m thick at the base. It is thickened 

 in or near the middle, and is here 4.5-6 ti in transverse diameter. It ends with a 

 regular or somewhat irregular terminal cone. Its irregularities appear to be 

 caused by the concrescence with it of the distal spines, which lie nearly parallel 

 to it. The distal ray bears sparse, irregularly distributed spines. The basal 



