HYALASCüS GIGANTEUS. 105 



usually somewhat shorter than the paratangentials. Not infre- 

 quently the proximal ray is also reduced to a knob-like rudi- 

 ment, so that the spicule takes the form of a stauractin (PL VIII., 

 fig. 9). On the other hand, tlie distal knob of the pentactins is 

 sometimes prolonged in varying degrees, leading to the regular 

 hexactinic form which is in fact occasionally met with. In all 

 cases the rays are rather slender, tapering but slightly outwards 

 and terminating with rounded or subconical tips ; the roughness 

 of surface, caused by rather unprominent microtubercles, is most 

 pronounced in the outer half of the rays and becomes gradually 

 weaker and inconspicuous towards the base. In size the dermalia 

 show a somewhat wide range of variation. As measured on the 

 paratangentials, the ray-length (half-axis) measures 120-200 // 

 with a breadth of about 7 h // at base. The plane of the four 

 paratangentials in a pentactinic dermalia is flat or just percep- 

 tibly arched. In some parts of the sponge surface, I have seen 

 the dermalia form a regularly quadrate-meshed lacework in which 

 the meshes measured on an average 110 f-f- in length of sides. 

 In other places they are evidently quite irregular in the mutual 

 relation of their paratangential rays. 



The gastralia (PI. VI IL, fig. 7) are similar but on the whole 

 much larger hexactins. The length of rays, as measured from 

 the spicular center, is mostly 165-385 /^. In the largest of the 

 spicules, the breadth of rays at base may reach 20 ij.. The six 

 rays are often unequally long, but I could not deduce the rule 

 that the free proximal ray is the longest. It is only occasionally 

 that a number of the gastralia are found so grouped as to form 

 approximately quadrate meshes with their paratangentials. The 

 distribution is for the most part quite irregular. As before men- 



