DENDY— CALCAREOITS SPONGES 89 



containing irregular subdermal cavities which lead into the wide inhalant lacunae. 

 The flagellate chambers are spherical, about 0-087 mm. in diameter and thicldy 

 scattered throughout the choanosome. The gastral cortex is thin ; its inner surface 

 nearly smooth and pierced by numerous exhalant openings. 



The arrangement of the skeleton oflers no pecuharities. The dermal skeleton 

 is composed of slender sagittal triradiates, tangentially arranged, with a few 

 scattered microxea. The gastral skeleton consists of slender sagittal quadriradiates 

 and triradiates. The skeleton of the chamber layer consists of much larger and 

 stouter triradiates, irregularly scattered, and of the inner portions of large oxea 

 whose outer ends are broken off. There are a few slender subgastral sagittal 

 triradiates and quadriradiates in the younger parts of the sponge, towards the 

 vent. There is an oscular fringe of trichoxea. 



1. Dermal triradiates (Fig. 10a). Sagittal, with long, slender, gradually sharp- 

 pointed rays. The oral rays usually curved, with wide oral angle. Size varying 

 a good deal, rays commonly somewhat unequal in length, averaging say about 

 0-28 by 0-017 mm. The arrangement of these spicules, except for the fact that 

 they all lie tangentially, is quite irregular. 



2. Gastral quadriradiates (Fig. 106). Sagittal, facial rays straighter and rather 

 more slender than those of the dermal triradiates, but of about the same length 

 and gradually sharp-pointed. Apical ray moderately long, slender, finely pointed, 

 nearly straight. As usual these spicules become more regularly arranged and 

 strongly alate towards the oscular margin, where also the paired rays become 

 much stouter than the basal ray. 



3. Gastral triradiates. Similar to the gastral quadriradiates but without the 

 apical ray. 



4. Subgastral sagittal radiates (Fig. 10c). Rays long and slender, gradually 

 sharp-pointed. Basal ray much longer than orals, say about 0-32 by 0-015 mm., 

 while the orals are only about 0-19 mm. long. Occasionally with a short apical 

 ray. Arranged as usual with the basal ray directly centrifugally. 



5. Triradiates of the chamber larger (Fig. lOd). Approximately regular, with 

 moderately stout, nearly straight, gradually sharp-pointed rays, varying a good 

 deal in actual size and in proportions ; measuring say about 0-35 by 0-03 mm. 



6. Large oxea (Fig. lOe). With their inner ends deeply implanted in the 

 chamber layer, or perhaps even projecting into the gastral cavity, and their outer 

 ends projecting obliquely upwards and outwards from the dermal surface. The 

 inner ends, where perfect, are gradually and finely pointed ; the outer ends are all 

 broken off short close to the dermal surface. The perfect spicule must be nearly 

 straight and very long. The portions remaining in the sponge may measure 

 nearly 2 mm. in length, with a thickness of about 0-05 nim. These spicules are 

 very numerous. 



