HYALONEMA (PRIONEMA) FIMBRIATUM. 299 



The stout, strongly curved, not centrotyle rhabd acanthophores (Plate 63, 

 figs. 27, 28) are rare. They are cyUndrical, thickened at both ends, and uni- 

 formly or irregularly curved. Their niiddle-part is smooth; their thickened ends 

 are spiny. These spicules are, measured along the chord connecting their 

 ends, usually 300-400 tx long, and about 18 m thick. The terminal thickenings 

 (tyles) are spherical and measure 35-50 n in diameter. 



The slender rhabd acanthophores (Plate 63, fig. 24) are usually slightly and 

 uniformly curved, 0.9-1.3 mm. long, and 5-15 m thick near the middle. Their 

 ends are more or less spiny and usually thickened. The terminal thickening is 

 sometimes 25 m and more in transverse diameter. A central tyle, 2-4 /u thicker 

 than the adjacent parts of the spicule, is usually present. 



The strongly curved, slender rhabd acanthophores (Plate 63, figs. 25, 26) are 

 rare. They are destitute of a central tyle and appear as strongly and irregularly 

 curved slender rods about 7 n thick. They are usually thicker at one end than 

 at the other, and thickened at both ends to unequal terminal tyles which are 

 spined, more or less spherical, and have a maximum transverse diameter of 

 25 M- The maximum diameter (length) of the curve formed by these spicules 

 is usually 300-500 /x. 



The basal anchor-spicules (Plate 62, figs. 5-11) are spined rods with an anchor 

 at the distal end. These rods have near the middle a maximum thickness of 

 72 /i, and are attenuated both proximally and distally ; proximally to a fine 

 point, distally to a thickness of 9-32 yu just above the anchor. The distal and 

 middle-parts of these rods are covered with straight, strongly inclined, inwardly 

 directed spines 10-25 n long. Proximally these spines become smaller and 

 finally disappear, so that the inner end-part of the spicule appears quite smooth. 

 The rod is traversed by an axial thread which terminates distally in the middle 

 of the anchor. The end is thickened, and from this thickening four short branch- 

 threads arise, which form a cross lying in a plane vertical to the rod or 

 anchor-shaft. The terminal anchor is 22-128 n high and 43-140 yu broad. It 

 consists of a stout, spherical centrum from which a number of anchor-teeth arise. 

 The centrum appears as a terminal tyle of the rod forming the anchor-shaft. 

 The teeth extend at various angles obliquely backward (upward) and outward. 

 They are sometimes 40 yu long, blunt, and very irregular and variable in position, 

 shape, curvature, and size. Some are bifurcate or otherwise branched. 



All the anchors observed lay altogether within the sponge. The stalk, 

 which no doubt was present in life, is absent in all the specimens. Probably 

 anchors of the kind described above take part in its formation. A few smooth 



