IiYALONEMA (PRIONEMA) AZUERONE. 
267 
paratangentially in the superficial membranes and occupy, singly or in bundles of 
two or three, the axes of the threads of the nets covering the afferent pores. 
Similar rliabds traverse the choanosome, singly or in bundles, in various directions. 
Most of these rhabds are centrotyle isoactine amphioxes. In some, one actine 
is reduced in length and terminally thickened ; these resemble tylostyles. Pentac- 
tine megascleres occur in the superficial parts of the lamellae. In the interior 
a few hexactine forms are found. Very numerous microhexactines and a few 
pentactine and diactine-derivates of these spicules are also found in the interior. 
Seven kinds of amphidiscs occur in this sponge : — not very numerous macramphi- 
cliscs with serrated anchor-teeth; very rare large mesamphidiscs with smooth 
teeth; very numerous medium mesamphidiscs, which, in places (Plate 58 , fig. 2 ), 
form quite dense masses; a few similar small mesamphidiscs; numerous slender- 
shafted regular micramphidiscs ; and two kinds of micramphidiscs, a larger and a 
smaller, which are stout- shafted, and generally more or less irregular. 
The superficial {dennal and gastral ) pinules (Plate 58 , figs. 3a, 10, 14, 15, 17, 
18, 20-22) observed were all pentactine. The distal ray is straight, 190-390 m 
long, and 5-9 m thick at the base. It ends with a very slender sharp-pointed 
terminal cone, and the whole of it, with the exception of its proximal and distal 
end-parts, is beset with spines. These spines are numerous, rather crowded 
and longest in the middle-part of the ray; they decrease in size both proximally 
and distally. The lowest arise nearly vertically; distally they become more 
and more inclined towards the tip of the ray. The longest spines of the middle- 
part of the ray usually enclose angles considerably less than 45° with the axis of 
the ray. These spines are conic, sharp-pointed, attain 25 m in length, 3 m in 
thickness, and are slightly curved, concave towards the tip of the ray. They 
are either simple, or bear one or two outwardly directed branch-spines, which 
sometimes reach a very considerable size (Plate 58 , fig. 18). The maximum 
thickness of the distal ray, together with the spines, is 22-36 m- The basal half 
of the lateral rays (Plate 58 , figs. 14, 15) is nearly cylindrical and smooth, the 
distal half conic and provided with somewhat sparse, quite large, broad, and low 
spines. The end is blunt. The lateral rays are 25-55 /z long. They appear to 
be longer in the gastral than in the dermal pinules; in the former they are usually 
about 40 m long, in the latter about 30 n. 
The canalar pinules (Plate 58 , figs, lb, 16, 19) are on the whole similar to 
the superficial ones but have more slender rays, a shorter distal ray, and fewer 
and smaller spines on the latter. It is also to be noted that they are not all 
pentactines, a few hexactine forms occurring among them. The measurements 
