T9I4-] ^- Annandale : Fauna Symhiotica Indica. 157 



tance thus attributed to the difference between the two types of 

 microscleres is not accepted by all spongologists. 



7:^. — A sponge common on Oyster-shells in Brackish Water. 



Fam. SUBERITIDAE. 



Subcrites aquae-dulcioris, sp. nov. 



Sponge. — The sponge forms a film not more than 2 mm. 

 thick, in most places quite flat but slightly raised in the neigh- 

 bourhood of the oscula, which are sparsely scattered on the 

 surface. The oscula are very small and can be closed completely ; 

 each is connected with a branching and occasionally anastomosing 

 system of superficial exhalent channels the roof of which is formed 

 by the dermal membrane. Except over these channels, the 

 external surface is minutely hispid. The dermal pores are minute 

 and occur in considerable numbers all over the membrane except 

 where it forms the roof of the exhalent channels. The subdermal 

 cavit}^ is ample, being supported by bunches of spicules. The 

 iiihalent canals run vertically downwards below the pores. The 

 colour of the living sponge varies from leaf-green to orange- 

 yellow; in specimens in spirit or dry it is dirty white. The 

 superficial area of the largest specimen seen did not exceed that 

 of a moderate-sized oyster- shell. 



Skeleton. — In living or carefully preserved sponges the skele- 

 ton consists of numerous plumose spicule-fibres which radiate 

 outwards and obliquely upwards through the sponge, their 

 general course being directed away from the oscula, towards 

 which their blunt ends pomt. At their external extremity, as 

 they approach the surface of the sponge, each fibre bears a large 

 bunch of vertical spicules with their sharp ends pointing upwards 

 and outwards. It is these bunches of spicules that support the 

 dermal membrane over the dermal cavity; only their tips pro- 

 trude through it. The floor of the superficial exhalent channels, 

 in which there are no bunches of spicules, is supported by single 

 spicules, which are directed outwards from the oscula and never 

 project vertically upwards. Theie are numerous loose spicules 

 lying parallel to the base of the sponge, especially in its lower 

 parts. The spicule-fibres are devoid of any binding substance 

 and the regular arrangement just described is apt to break down 

 if specimens are not carefully preserved. In this case the skele- 

 ton-fibres often disappear almost completely, but the terminal 

 bunches are more consistent. 



Spicules. — The only spicules proper to the sponge are 

 macroscleres, but if, as is often the case, it is growing in close 

 contact with Cliona vastifica, Hancock, the zigzag microscleres of 

 that sponge are apt to intrude into it. The macroscleres are of two 

 sorts, amphioxi and tylostyles; the former are, however, ex- 

 tremely scarce and should be regarded as abnormalities. They 

 are slender and always more or less distorted. With few excep- 



