HYALONEMA (HYALONEMA) AGASSIZI. 177 



small rhabds are met. Outside the axial column, however, only the smaller 

 ones have been observed. 



In the interior the uncinates are not very numerous and are irregularly 

 scattered. Of amphidiscs both macramphidiscs and micramphidiscs occur in 

 the interior. The former are very scarce, the latter, which appear chiefly to 

 occupy the walls of the efferent canals, exceedingly numerous. The micro- 

 hexactines and their derivates are, in the interior, rather frequent, but not nearly 

 so abundant as in the superficial region. The spheres appear to be restricted 

 to the axial column, where they occur singly or, more rarely, in clusters. They 

 are rather numerous in form A and have also been found in form D. 



In the specimens of form A, B, and in two of the specimens of form F the 

 stalk is more or less intact. It is in these forms composed of stouter and more 

 slender rods, broken off at the lower, distal end. In the specimen of form A 

 the stalk is over 40 cm. long and now consists of twenty spicules; in life there 

 may have been more. The spicules composing it are very distinctly spirally 

 twisted, like the strands of a rope and also similarly entwined. The twist has 

 the same direction in all. Progressing from the proximal to the distal end the 

 spiral curvature is in the direction of the movement of the hands of a watch. 



The stalk-spicules extend for some distance upwards into the sponge-body, 

 and they are, in the basal part of the latter, surrounded by masses of acantho- 

 phores. These are stout-rayed, usually terminally spined tetractines (staurac- 

 tines), derivates of these spicules, more or less spiny pentactines, modified 

 pinules, and modified rhabds with spiny ends. In the basal part of some of the 

 specimens spheres also occur. In the specimens of all the forms with the excep- 

 tion of those of forms E and F, slender-rayed, long-spined spicules with four to 

 six rays also occur just below the surface of that part of the body from which 

 the stalk arises. Their absence in forms E and F is probably due to the frag- 

 mentary nature of the specimens of these forms. 



The dermal pinules (Plate 42, figs. 20-23, 25-30, 37b, 42b) are nearly all 

 pentactine; only a few are hexactine. Their distal ray, in form A (Plate 42, 

 figs. 25-28, 35, 36), is straight, 93-110 m long, usually 94-107 m, on an average 

 100.4 fi; and, at the base, 4.4-7 m thick, usually 4.5-6.7 m- Above it thickens, 

 and it ends with a well-developed, smooth, terminal cone 6.5-11 n thick, usually 

 8.5-9 n. The proximal, basal part of the ray and its terminal cone are free from 

 spines; the rest of it, usually about 60% of its length, is covered with spines. 

 The most proximal spines diverge strongly, and are often nearly vertical to the 

 ray. Distally they become more inclined towards the tip, and the uppermost 



