56 



GEODIA VARIOSPICULOSA. 



Shape and size. The specimen of var. micraster (Plate 17, fig. 41) is tuberous 

 and measures 42 mm. in length, 34 mm. in breadth, and 24 mm. in height. The 

 surface is somewhat undulating. Here and there slight, abrupt, step-like 

 changes of level of about 0.3 mm. are observed in it. In one place there is a 

 round hole, a little over 1 mm. wide. This appears to be the entrance to a 

 tubular cavity occupied by an annelid, and not an osculum. Apart from this 

 no apertures are visible. Large parts of the surface are occupied by shallow 

 pits, the centres of which are less than 1 mm. apart. A dense fur of minute 

 spicules, about 100-200 /< high (Plate 18, fig. 26c), visible only with the micro- 

 scope in sections, covers the whole of the surface. Besides this, remnants of a 

 sparse fur of large spicules, 2-3 mm. high, are observed in unexposed places. 



The specimen of var. intermedia (Plate 17, figs. 39, 40) is thick oval, slightly 

 constricted near one end, 22 mm. long and 15 mm. broad. It was attached at 

 one side. The surface is continuous, without undulations or step-like changes 

 of level, free from apertures visible to the eye, and for the greater part covered 

 with shallow pits, more conspicuous on one side than on the other. Where 

 these pits are more conspicuous their centres are 1-1.2 mm., where they are less 

 conspicuous 0.6-0.9 mm., apart. A low dense spicule-fur is also present in this 

 variety, but there are hardly any traces of a sparse, high spicule-fur. 



The colour (in spirit) of var. micraster is nearly white, that of var. 

 intermedia light coffee-brown. 



The superficial part of the body forms a cortex composed of three layers: 

 an outer dermal layer free from sterrasters, a central sterraster-armour layer, 

 and an inner fibrous layer containing but few sterrasters or none at all. In the 

 pits the dermal layer is considerably thickened, on other parts of the surface it 

 is very thin. The sterraster-armour layer is chiefly composed of sterrasters. 

 The connective-tissue fibres radiating from the sterrasters and connecting them 

 with each other are very conspicuous. Around the proximal parts of the radial 

 canals which penetrate the sterraster-armour rather extensive zones of chonal, 

 fibrous tissue, free from sterrasters, occur (Plate 18, fig. 21). The sterraster- 

 armour layer and the dermal membrane are together 0.5-1 mm. thick. Sections 

 show that the above mentioned step-like changes of level in the surface of var. 

 micraster are caused by abrupt changes of thickness of the sterraster-armour 

 layer, the lower limiting surface of this layer passing smoothly and unchanged 

 beneath the steps. The fibrous layer of the cortex (Plate 18, figs. 21, 26) is for, 

 the most part over 1 mm. thick and in many places excavated by cavities. 

 The walls separating these are chiefly composed of fibres arranged obliquely 



