342 HYALONEMA (OONEMA) DENSUM. 



and perforated by numerous broad-oval efferent apertures 0.2-0.9 mm. wide 

 (Plate 95, fig. 3). A pointed, A'ery eccentrically situated gastral cone 8 mm. 

 high and, at the base, 6 mm. thick arises from it. The conical body is slender 

 and has no pores visible with the unaided eye. Its surface is to be considered 

 as the dermal face of the sponge. Its lower end is torn off. 



The colou7- in spirit is dirty light brown. 



Canal-system. In the choanosome more or less radial canals, sometimes 0.8 

 mm. wide, are observed. Indications of elongate, perhaps tubular, flagellate 

 chambers 30-70 m broad are observed in the sections. 



Skeleton. The whole of the surface is covered with a dense pinule-fur 

 (Plate 95, figs. 1, 2). • Between the proximal parts of the freely protruding 

 distal rays of the pinules forming it are met small macramphidiscs, mostly 

 with the shaft in a radial position. The dermal and gastral membranes are 

 supported by the lateral rays of the superficial pinules, paratangential centro- 

 tyle amphioxes, and the lateral rays of hypodermal or hypogastral pentactines. 

 Masses of microhexactines and some small macramphidiscs occur in and just 

 below these membranes. A good many large micramphidiscs, dense masses 

 of microhexactines, and a few canalar pinules occur in the canal-walls. The 

 micramphidiscs appear to be restricted to the efferent canals. Apart from these 

 canalar spicules, one finds in the interior a few large macramphidiscs, hexactine 

 megascleres, and small micramphidiscs, numerous ordinary small choanosomal 

 amphioxes, and some large axial amphioxes forming the upper continuation 

 of the stalk. In the lower part of the sponge-body numerous acanthophores 

 are added to these spicules. These extend remarkably far up. The upper 

 acanthophores have long, slender, and usually fairly straight and not very spiny 

 rays. In the lower acanthophores the rays are either reduced in length, stout, 

 and very spiny, or long, slender, not particularly spiny, and more or less, often 

 considerably curved. 



The dermal pinules have a distal ray 230-855 n long. The length frequency- 

 curve of their distal rays has a very marked depression at about 530 m, and two 

 perfectly distinct elevations at 370 and 650 n. I therefore distinguish two kinds 

 of dermal pinules, a large and a small. 



The large dermal pinules (Plate 95, figs. 1, 15, 19, 20) are pentactine. Their 

 distal ray is straight, 560-855 m long, most frequently about 650 m, and 12-23 n 

 thick at the base. It ends with a short and stout terminal cone, and bears spines 

 which extend quite down to its base, or nearly so. The lowest spines are very 

 short, stout, conical, and vertical; distally the spines become larger and more 



