154 HYALONEMA (HYALONEMA) OBTUSUM. 



bent to one side (Plate 34, fig. 3c). The frill .surrounding it terminates with a 

 fairly circular margin which lies in the level of the summit of the cone. The 

 gastral cavity appears as a narrow fissure 5-12 mm. deep but only 0.4-1 mm. 

 wide (Plate 33, fig. 16; Plate 34, fig. 3b) separating the gastral cone from the 

 marginal part of the sponge-body. 



The surface of the cone, and the inner face of the upper tubular marginal 

 part of the wall surrounding the gastral cavity are smooth and destitute of aper- 

 tures of any kind, the efferent openings being restricted to the bottom of the 

 fissure-like gastral cavity. The intact parts of the outer surface exhibit a fine 

 reticulate structure with meshes about 0.7 mm. wide (Plate 33, fig. 15). 



The colour of the specimen of var. robusta in spirit is rather dark reddish 

 brown, that of var. gracilis light greenish brown. 



Canal-system. The state of preservation of the specimen of var. robusta 

 renders it impossible to say anything about the canal-system. In the specimen 

 of var. gracilis subdermal cavities (Plate 34, figs, lb, 3, 4, 19c), mostly 0.3-0.7 

 mm. high and 0.2-0.5 mm. broad, are spread out below the dermal membrane 

 (the outer surface) . These cavities are generally separated from each other by 

 thin partitions. From most of them small afferent canals take their origin; 

 some are directly continued in large afferent canal-stems, 0.3-0.7 mm. wide, 

 which extend somewhat tortuously towards the interior, and ramify in the 

 central part of the sponge. Occasionally junctions of two such afferent canal- 

 stems have been observed. The choanosome, that is the region occupied by the 

 flagellate chambers, does not extend, for the most part, beyond the level of the 

 floors of the subdermal cavities. In a few places only broad, conical groups of 

 flagellate chambers rise between adjacent subdermal cavities, up to a distance 

 of only 0.1 mm. from the outer surface. 



The individual flagellate chambers appear to be broad oval or nearly 

 spherical, and attain a maximum diameter of 60-100 /z (Plate 34, fig. 2). The 

 efferent canals join to form canal-stems up to 1.2 mm. wide, which, as above 

 mentioned, open out into the bottom of the narrow, fissure-like gastral cavity. 

 The larger of these canals are considerably contracted at the mouth. 



The skeleton of var. gracilis. The outer surface is covered with dermal 

 pinules, micramphidiscs, and small macramphidiscs. Most of the pinules are 

 pentactine, some hexactine. Their paratangentially extending lateral rays lie 

 in the dermal membrane; their radially extending and freely protruding distal 

 rays form a fur about 150 ^ high (Plate 35, fig. 24). The micramphidiscs 

 are, in some places at least, exceedingly numerous. They seem to be quite 



