1867.] DR. J. E. GRAY ON SPONGES. 547 



Fam. Xenospongiad^. 

 Xenospongia, Gray, P. Z. S. 1858, p. 230. 

 Xenospongia pateluformis. Gray, ib. Rad. pi. xii, B.M. 



Hab. Torres Straits. 



The genus Halicnemia(QoviQvh. B. S. i. p. 184, t. 32. f. 363, 364, 

 ii. t. 9^) has the same form as the former. It has a small pebble 

 imbedded in the centre ; but, from the description and the figures, I 

 have little doubt that it is distinct from the above, though it may 

 belong to the same family. It contains many imbedded short pin- 

 shaped spicules, and some oblong tubercular bodies like ovisacs (see 

 f. 364). But there are many differences in detail that show it must 

 be a very distinct genus ; for example, the oscules are numerous on 

 the lower, concave surface, the upper surface is covered with extra- 

 neous matter, and the lower one clear of such impurities. 



Section II. Chlamydospor^. Reproduction chiefly by ova con- 

 tained in defined ova-cells or " ovaria,'' strengthened with 

 siliceous spicules, sometimes at length becoming solid spheres 

 formed of siliceous spicules radiating from a central point. 



Order VI. SPHiEROSPONGIA. 



The ovisac cells composed of closely packed fusiform spicules di- 

 verging from the centre, which, when the ova are emitted, extend 

 internally and fill up the cavity, forming the ova-cells into nearly solid 

 balls, formed of spicules diverging from the centre to the circum- 

 ference, which are congregated together, and form a hard external 

 coat to the sponge. 



Fam. 1. Geodiad.^. 



Sponge massive, fleshy, cellular within ; pores with a regular con- 

 strictive valve. Ovisacs subglobose or oblong, with a thick coat 

 formed of spicules in lines, radiating from the axis to the circum- 

 ference, and at length becoming solid, congregated on the outer sur- 

 face, or scattered in the flesh. Spicules elongate; the larger ones 

 with two or three expanded or recurved branches on the outer ends ; 

 smaller ones simple, often extending beyond the surface. 



I. The ovisacs forming a thick external covering to the sponge. 

 I. Pachymatisma, Bowerb. B. S. i. p. 171, ii. p. 51. 



Sponge massive, irregular. Ovisacs forming a continuous external 

 covering to the sponge. Spicules uniform, very slender ; outer ends 

 with two or three diverging branches. 



Pachymatisma johnstonia, Bowerb. ib. ii. pp. 51, 1/2, f. 15, 

 16, 17, 20, 21, 45, 46, 93. 158, 159, 330, 331, 332, 353. 



Halichondria johnstonii, Bowerb. B.M. 



