292 MARINE BIOLOGY OF THE SUDANESE RED SBA. 
(?) HALISARCA sp. 
Two mussel-shells occur in the collection covered with an extremely thin 
film of sponge, which apparently belongs to this genus. The chambers were 
few in number and very long, and large numbers of embryos occurred in the 
sponge. No other details could be made out. 
‘The specimens were obtained from a buoy in Suez Harbour. 
Order TRIAXONIDA. 
No Hexactinellid sponges were obtained by Mr. Crossland, but Schulze (27) 
describes the following three species from the deeper parts of the Red 
Sea :— 
Aulocystis grayi (Bowerbank). 
Aulocystis citteli (Marsh & Mayer). 
Tretocalyxe pole, Schulze. 
Order TETRAXONIDA. 
Non-Calearea in which the fundamental form of the spicule is tetraxonid 
and tetractinellid ; the spicules may, however, be more or less reduced, and 
also to a greater or less extent replaced by spongin or even sand. 
Sub-Order HOMOSCLEROPHORA. 
Tetraxonida in which megascleres and microscleres are not sharply 
differentiated from each other, and no triznes are developed. 
Family PLAKINIDA. 
Homosclerophora in which no distinct cortex is developed. 
PLacoRTIS SIMPLEX, Schulze. 
Synonymy :— 
1880. Placortis simplex, F. E. Schulze (28). 
1895. Placortis simplex, Topsent (34). 
A single small somewhat irregular specimen of this sponge was obtained 
on Suez mud-flats, measuring 15 mm.x8 mm. The colour is yellowish 
white. The skeleton is exactly like Schulze’s description. 
Distribution. Red Sea, Mediterranean. 
Sub-Order ASTROTETRAXONIDA, Hentschel (15). 
Tetraxonida which possess astrose microscleres, or are derived from 
such aster-possessing forms. 
