STAUROCALYPTUS HAMATUS. 113 



Its lower, concave side fits the dorsal side of a crustacean, apparently a species 

 of Dicranodroniia, whicK firmly holds the sponge on its back by the dorsally 

 du-ected, last pair of thoracic extremities. In its original position the sponge 

 completely covered the Dicranodroniia dorsally (Plate 18, fig. 14). Seen from 

 above (Plate 18, fig. 5) or below (Plate 18, fig. 6) the sponge appears oval in 

 outline, with a protuberance at one end. It is 35 mm. long and 28 mm. broad. 

 The wall of the inverted cup, formed by it, is about 3 mm. thick. Scattered 

 pores are observed both on the free upper convex side and the lower concave side 

 which rested on the back of the Dicranodromia. Those of the upper side are 

 mostly oval, with a maximum measurement of 1 mm. in length and 0.5 in breadth. 

 Those of the lower side are relatively broader, more nearly circular, and reach 

 1.5 mm. in diameter. Large prostal rhabds protrude both from the upper and 

 the lower side. 



The colour in spirit is light brown. 



General structure. I found a few remnants of a dermal membrane both on 

 the concave, lower, and the marginal part of the convex, upper side. Of a 

 gastral membrane no trace could be detected. The remnants of the soft parts 

 in the interior indicate that the sponge has sac-shaped flagellate chambers, 80- 

 100 M long and 50-70 ^ broad. 



Skeleton. Spicule-bundles, 40-200 ^ thick, traverse the sponge. These 

 bundles appear to be most numerous just below the lower, concavq face of the 

 sponge, where they extend chiefly paratangentially. They are composed of 

 rhabds — of small rhabds only, or of a large rhabd accompanied and more or less 

 enveloped by numerous, coinital, small rhabds. Besides the rhabds forming 

 the bundles, isolated rhabds also occur in large numbers. Oxyhexasters, hemi- 

 oxyhexasters, and oxyhexactines with straight rays and end-rays, oxyhexactines 

 with terminally curved, hook-like rays, and discoctasters of various size are very 

 numerous. The last appear to be much more frequent in the interior than near 

 the surface of the sponge. Small discohexasters, and hemioxyhexasters with 

 rays, either all hook-like or partly hook-like and partly straight, are met with 

 in smaller numbers. Hypodermal pentactines and a few triactine megascleres 

 occur at, or just below, the surface. On those parts of the surface where rem- 

 nants of the dermal membrane are left, spiny rhabds are observed. Most of 

 these are simple diactine rhabds. Some are centrotyle, and a few possess, 

 besides the two properly developed rays, short rudiments of one or two further 

 rays. These spicules and a few angular diactines and stauractines, similar in 

 regard to size and spinulation, found in the spicule-preparations, I consider as 



