8 LEUCETTA. LEUCOETIS. 



canals measure 0-4-0-8 milHm. in diameter. The exhalants are more irregular, 

 and join to form canals with a diameter varying from 0-6-0-2 millim., which 

 open with circular pores of the same width into the gastral cavity. These pores 

 are in some places 1-5-2-5 millim. distant ; in others they are further apart. 



The skeleton is composed of dense masses of triact spicules ; these are equi- 

 angular. The rays of the smaller ones measure O-lGOxO-12 on an average, 

 those of the large ones 0-640 x 0-02 millim. The spicules of the small variety 

 are larger than those observed by Haeckel, whilst the large ones are not so 

 numerous. 



Geographical Distribution. — East coast of Australia: Port Jackson 

 (Ramsay). 



Genus LEUCORTIS. 

 Leuconidse with triact and diact spicules. 



Leucortis elegans, n. sp. 



The sponge consists of a meandric, much and irregularly curved lamella 

 with a very uneven surface and numerous oscula. This structure has 

 faint resemblance to the human brain, and may attain a leugth of 130, 

 width of 100, and height of 40 millim. The lamella appears, if studied 

 more closely, to surround a very extensive cavity, which is the common 

 gastral cavity of the sponge, and in counexion with the outer water by 

 numerous oscula. The lamella is accordingly the hody-ivall. The dredge 

 frequently brings up fragments of this extremely tender structure only — small 

 pieces of the lamella. Of these the one side is the inner (gastral) surface and 

 the other the outer one. This lamella, or the body-wall as I shall henceforth 

 designate it, is about 0-8-1-2 millim. thick, so that the proportion of the 

 thickness of the body-wall to the diameter of the body-cavity is a very unusual 

 one, 1 : 30 or more. This accounts for the extreme laxity and tenderness of 

 the whole structure. The oscula are generally situated on raised irregular 

 ridges ; they are circular and frilled, and have a diameter of 1 millim. The 

 frill is about 1 millim. high. Both the inner and outer surfaces are smooth ; 

 macroscopically the two can be distinguished because the inner surface 

 appears less dense than the outer. The sponge is in spirit white, with a yellow 

 tinge. The subdermal cavities are highly developed. The inhalants are irregular 

 and small. The exhalants join to form large canals which extend taugentially 

 through the thin body-wall and often undermine the gastral surface for some 

 distance ; they open into the gastral cavity with very large, circular pores 2-4 

 millim. in diameter, which are not numerous. The exhalaut canals in the 

 middle of the budy-wall measure l-l'o millim. in diameter; those below tlie 



