124. LEIOSELLA. 



similar low cones on the surface, with converging sense-cells. Professor 

 Stewart's beautiful sections show that very long, high, conic, pointed pro- 

 tuberances are present on the surface of the living sponge, and there can be 

 no doubt that the low cones are simply protuberances of this kind shrunk 

 through the influence of the hardening reagents employed in preparing the 

 sections. I consider myself justitied, therefore, in assuming that also in 

 Leiosella silicata the low cones are retracted synocils, entirely similar to those of 

 Calcareous sponges. The synocils are in the living sponge probably 0'08 miUim. 

 long, and at the base 0-017 miUim, thick ; they are covered with very thin ecto- 

 dermal pavement-cells, which appear drawn out to form curved plates. Nuclei 

 can be discerned in these cells. In the synocil slender spindle-shaped sense- 

 cells are found, which diverge below. The distal ends of these extend up into 

 the summit of the synocil. Some of these cells are higher up in the synocil 

 than others, so that their thickened centres, in which the very elongate oval 

 nuclei are situated, do not lie at the same level. The proximal ends of these 

 cells are probably in connection with ganglion-cells below. I have, however, 

 failed to observe the latter. The sense-cells themselves differ from those found 

 in the synocils of Calcareous sponges, inasmuch as they are slender and regu- 

 larly spindle-shaped, and their two ends are similar. In the synocils of Calca- 

 reous sponges these cells are rather different, and often appear multipolar, 

 somewhat pear-shaped, with one very long centrifugal process. I cannot say 

 whether synocils are more widely distributed in this genus. I have not 

 observed them in any other species. 



The skeleton of the surface consists of scattered spicule-fragments and sand- 

 grains, and a network of fibres 0-01 millim. thick, with polygonal, angular 

 meshes, 0*15 millim. wide. 



The main fibres of the supporting-skeleton are irregularly curved and often 

 abruptly bent at the joining points of the connecting-fibres, so as to form a 

 zigzag line ; they are 0-04-0"066 millim. thick, knotty, and cored with irre- 

 gularly disposed spicide-fragments and a few sand-grains. The connecting- 

 fibres are 0-016-0-025 miUim. thick, and contain comparatively abundant 

 spicule-fragments in their axis. These are always disposed regularly longi- 

 tudinally, and never render the surface of the fibres uneven, as they do in the 

 main fibres. The meshes of the network formed by the connecting-fibres are 

 iri'egularly polygonal, somewhat rounded, and on an average 0-09-0*18 millim. 

 wide. 



Geographical Disteibution. — North coast of Australia : Northern Terri- 

 tory, S. A. (Haacke) ; Torres Straits {Maclmy). East coast of Australia : Port 

 Jackson, N. S. W. (Lendenfeld, llamsay). 



