82 OKHAMANDAL MARINE ZOOLOGY REPORT— PART II 



(Fig. 7c). The dermal cortical skeleton is made up of the dermal triradiates 

 (Fig. 7a) arranged tangentially, and of the outer rays of subdermal pseudosagittal 

 triradiates (Fig. 7e). The tubar skeleton approaches but does not completely 

 realise the inarticulate type, the stout subgastral sagittal triradiates being 

 succeeded centrifugally by two or three other sagittal triradiates very similar 

 to « themselves (Fig. Id). The subdermal pseudosagittal triradiates (Fig. 7e) are 

 much slenderer than the subgastral spicules (Fig. 7c), and their centripetally directed 

 rays are commonly grouped in bundles which meet and overlap the opposing basal 

 rays of subgastral or tubar sagittals. Around the oscular margin there is a narrow 

 band of strongly alate triradiates which occasionally develop a short apical ray. There 

 appears to be no oscular fringe of oxea, but a few stout oxea (Figs. 7/, 7/', If") are to be 

 found penetrating the sponge wall more or less at right angles, and often projecting 

 from the dermal surface. 



The spicules may be grouped under the following heads : — 



1. Dermal triradiates (Fig. 7a). Nearly equiangular but commonly inequjradiate, 

 with indications of a sagittal character. There is no definite orientation, but what 

 appear to be the oral rays are sometimes more or less crooked while the basal ray is 

 straight. All rays gradually and sharply pointed. Size very variable. In a typical 

 example the basal ray measured about 0-42 by 0-025 mm., and the orals 0-36 by 

 0-025 mm. and 0-3 by 0-025 mm. respectively. 



2. Gastral triradiates (Fig. 7b). Very similar to the dermal triradiates but con- 

 siderably smaller. In a typical example the apparently basal ray, which was straight, 

 measured about 0-16 by 0-02 mm., and the orals, which were very slightly crooked, 

 each about 0-24 by 0-015 mm. Towards the osculum these spicules become very strongly 

 sagittal and exhibit a definite orientation, the oral rays being extended in line with 

 one another and parallel to the oscular margin, while a short apical ray is occasionally 

 developed. 



3. Subgastral sagittal triradiates (Fig. 7c). Stout, with oral rays slightly recurved 

 towards the basal, which latter is straight. Oral rays bent towards one another in a 

 plane parallel to the gastral surface, so as to give rise to a deceptive appearance of 

 inequality according to the point of view.' All rays gradually sharp-pointed. In a 

 typical example the basal ray measured 0-51 by 0-04 mm., the orals apparently 0-37 by 

 0-035 and 0-25 by 0-035 mm. respectively. 



4. Tubar triradiates (Fig. 7d). These are not really distinguishable from the 

 subgastral sagittal triradiates except by their more distal position. The most 

 distally situated show less curvature of the oral rays, and are of smaller size, but they 

 are connected by intermediate forms with the typical subgastral sagittals. 



5. Subdermal pseudosagittal ^ triradiates (Fig. 7e). Conspicuously smaller and 



^ Actual inequality may, however, occur to a considerable extent. 

 - For a discussion as to the nature of these spicules vide infra, p. 86. 



