1122 A MONOGRAPH OP THE AUSTRALIAN SPONGES, 



mm., in thickness. The cylindrical Gastral cavity is covered 

 with small pores, rather narrow. The body-wall measures 

 1-H mm. in thickness. 



Skeleton. Most of the spicules are Quadriradiates of middling 

 size. These are covered by a clothing of Triradiates. The latter 

 form a dense dermal layer. The Quadriradiates are mostly 

 sagittal or irregular. Their rays measure 0-3 — 0-6 x 0-03— 0-05. 

 The dermal Quadriradiates are situated as in LeucaltiS Helena : 

 three rays in the surface tangental ; the fourth radial, pointing 

 centripetally. The tangental rays of these spicules are sagittal 

 in themselves, the unpaired angle measuring 160 — 180° 



The Tiiradiates are irregular, the mean measurement of their 

 rays is 0-15—0 3 x 0-008— 0-015. The inner layer is formed by 

 Triradiates and Quadriradiates. 



The principal difference between this species and LeucalMs 

 Helena lies in the distribution of the Triradiates, which in the 

 latter do not form sheaths around the parenchymal Quadriradiates. 

 Ridley (I.e.) has established the variety Leucaltis bathybia var. 

 australis for a slightly aberrant form obtained by the Alert. He 

 describes his variety as follows : — A small low marine specimen, 

 with a small lateral unarmed vent and very reduced cloacal cavity. 

 The Quadriradiates are sagittal, those of the outer surface very 

 large. Diameter of rays about 0.04 mm. The facial angle nearly 

 180°, the apical ray in the same plane as the laterals. The deep 

 Quadriradiates have a somewhat smaller facial angle and more 

 slender rays and the apical ray often projects well forward. Eays 

 almost straight. The Triradiates form a thin layer on the inner 

 wall where their rays measure only about 0-01 mm., in diameter, 

 they have a facial angle of about 160°, in the deep parts they are 

 Bubregular, sparsely scattered amongst the Quadriradiates and the 

 ray measure about 0-02 sometimes 0-025 in diameter, rays approse 

 straight: 



Colour : White. 



The main feature of this variety lies in the large size of the 

 profound Triradiates, and in the massive form of the Sponge. 



Locality \ Eed Sea, Perim, Siemens, Djeddah, Miklouho- 

 Macldy ; East Coast of Australia, Port Jackson, Alert. 



