324 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



ous radially placed megascleres and by bundles of the same, and 

 there are megascleres abundantly scattered, some in tracts, through 

 the interior. Some of the peripheral radial bundles are prolonged 

 for a considerable distance into the interior, but there is no central, 

 or axial, skeletal aggregation comparable to that occurring in 

 Geodinelle cylindrica Thiele. An axial aggregation of megascleres 

 (reduced triaenes and rhabds), but a very loose one, occurs also in 

 the other recorded species of the genus, G. robusta (Lendenfeld, 

 1910, p. 208). 



The reduced triaene is a constant and abundant constituent of the 

 peripheral radial skeleton, also of the tracts and scattered skeleton 

 of the interior. The dominant megasclere of the interior is the large 

 oxea ; and this spicule is abundant also in the peripheral radial skele- 

 ton. 



Spicules. — 1. Reduced triaene, represented by a monaene with de- 

 generate clad or by a subtylostyle or style (pi. 47, fig. 4) ; about 2 

 mm. long, 40-44 \i thick. 



The distal (cladal) end of the spicule is generally enlarged, but 

 only slightly so, sometimes not at all enlarged (fig. 4A). In general 

 there are no signs of clads, not even a branching of the axial canal at 

 the distal end (fig. 4^). Nevertheless spicules not infrequently occur 

 in which an extremely vestigial clad is present, monaene condition 

 (figs. 4 a, b, c, d, e, /). The clad may be only a rounded protuber- 

 ance on one side of the head, or a pointed and more definite pro- 

 tuberance. The axial canal of the clad is not straight, and looks 

 as if made up of a row of dots, which probably means that the canal 

 has not a uniform diameter. The proximal end of the reduced 

 triaene is pointed. 



In the peripheral part of the sponge the reduced triaenes lie in 

 the usual position occupied by triaenes in this family. The spicule 

 as a whole (rhabdome) is radial, and the distal end is commonly 

 just below the sterrastral layer, sometimes in the layer. 



2. Oxea, 2.4^3 mm. by 48 jjl; in peripheral radial skeleton and in 

 interior. 



3. A long slender oxea, about 12 \i thick; not quite straight; occur- 

 ring in some abundance in the radial skeleton, often in sheaves; along 

 with the stouter megascleres or separately from them; sometimes, 

 perhaps always, passing entirely through the cortex and projecting 

 beyond the surface. 



4. Sterraster, ellipsoidal and somewhat flattened; 200 [x long, 164 

 p wide, 130 p, thick. Ends of rays small, stellate, leaving the usual 

 reticulum of lines between them. Sterrastral layer about 1800 |jl 

 thick; the spicules together with developmental stages also scattered 

 in the choanosome. Developmental stages plentiful, showing that 

 the spicule develops in the usual way. 



