HYALONEMA (PRIONEMA) FIMBRIATUM. 
299 
The stout, strongly curved , not centrotyle rhabd acanthophores (Plate 63, 
figs. 27, 28) are rare. They are cylindrical, thickened at both ends, and uni- 
formly or irregularly curved. Their middle-part is smooth; their thickened ends 
are spiny. These spicules are, measured along the chord connecting their 
ends, usually 300-400 fx long, and about 18 n 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 n 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 /x 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 n, and are attenuated both proximally and distally; proximally to a fine 
point, distally to a thickness of 9-32 n just above the anchor. The distal and 
middle-parts of these rods are covered with straight, strongly inclined, inwardly 
directed spines 10-25 m 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 m high and 43-140 ^ broach 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 m 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 
