Briefly, the three genera of Scleritoderniidce ;irc thus char- 

 acterised : — 



Microscleroderma, ectosomal spicules minute sigmaspires. 

 Sclcritoderma, ectosomal spicules minute sigmaspires, 



and microstrongyles (? large sigmaspires). 

 Acicuiites, ectosomal spicules rhahdi only ( ? modified 



sigmaspires). 



Family AzoricidsB. 



Lithobactrum,* j^'en. nov. 



Azoricida; massive club-shaped, with uniformly distributed 

 pores at the sides, and with numerous small oscules on the 

 rounded summit ; with fine parallel incurrcnt canals radiating 

 horizontally inwards from the pores, and excurrent canals 

 passing vertically upwards to the oscules. 



Lithobactrum forte sp. n. 

 Plate iv., iij^s. 5, .Oa-g. 



Sponge with characters of the genus. 



Pores nearly circular, .25 mm. in diameter; oscules, .75 to 

 I mm. in diameter, flush with the surface, sharp edged, oval or 

 circular, in groups with an obscurely radiating arrangement. 



Skeleton composed of monocrepid desmas, forming a compact 

 lining to the canals, but looser between the canals. 



Spicules.- -Desmas of the usual monocrepid type (Fig. 5c-f), 

 450 X 50 /' ; crepis 70 a'. 



Amphityle 992 x 8 m, with long oval heads, one larger than 

 the other, the larger being 14x8 m, and the smaller 10x5 /'. 



Other kinds of monaxon spicules (oxeas, styles, tyles) occur, 

 but are very probably adventitious. The amphityles occur 

 deep in the sponge, and intimately associated with the desmas. 



Colour, glistening white. 



Locality: O'Neil Peak, Natal Coast, bearing N.N.W. ^ W., 

 distant 8 miles ; depth, 55 fathoms ; bottom, broken shells. 



Following the example of Schmidt and Sollas, the characters 

 of the genus have been based on the external form and the 

 arrangement of the pores, oscules and canal-system ; and as 

 Azoricid sponges are devoid of an ectosomal skeleton and of 

 niicroscleres, there is not much else to fall back upon. 



There are two specimens of this fine sponge. The larger 

 grows from an expanded base (7x5 cm.), immediately above 



• Ai^of stone, /^(ixirpot- club. 



