146 CEYLON PEARL OYSTER REPORT. 



(VI 3 millim. The fibres are compact, but the arrangement of the spicules in them is 

 very confused and there is no visible spongin. Many spicules occur scattered 

 irregularly between the fibres, so that the whole skeleton forms an almost solid mass 

 of spicules. There is no special dermal skeleton. 



Spicules. Stout, fusiform oxea (Plate IX., fig. 9); slightly curved and usually 

 sharply and fairly gradually pointed ; size when fully developed about 0"24 millim. by 

 0"02 millim., but with numerous smaller forms which are presumably young. 



This species is evidently very closely related to Thiele's Petrosia imperforata from 

 Celebes (39). 



R.N. 138, 138a (both from deep water off Galle and onwards up West Coast of 

 Ceylon). 



Halichondria, Fleming. 



Renierinse in which the skeleton consists of a confused reticulation of long and slender 

 oxea (or strongyla) with little or no spongin ; the spicules sometimes associated 

 in ill-defined bands or fibres. 



I have already indicated the doubt which exists as to the true relationship of this 

 genus. Possibly it is, as at present understood, of polyphyletic origin, including 

 species derived from several ancestral forms by loss of microscleres. 



Halichondria panicea, Johnston. 



[For literature and synonymy vide Ridley and Denuy (1) and Dendy (2).j 

 This widely distributed species is represented in the collection by two well 

 differentiated form-varieties, so that it seems desirable to distinguish them by varietal 

 names. In both varieties many of the more superficial oxea are arranged more or less 

 at right angles to the surface, with their apices projecting to a greater or less extent, 

 thus making an approach to the genus Trachyopsis. In both the full-grown spicules 

 measure up to about l'O millim. in length and are of the usual Halichondria type. 

 Their arrangement in the interior of the sponge is quite irregular and confused. 



Halichondria panicea, Johnston, var. megalorhaphis, Carter. 

 1881, Amorphina megalorhaphis, Carter (5). 

 This variety is irregularly encrusting, growing out into lobose or digitiform 

 processes, and with small scattered vents. 



R.N. 87, 231, 248 (all from deep water off Galle and onwards up West Coast). 



Halichondria panicea, Johnston, var. heinispherica, nov. 

 Tins variety is massive and compact, more or less hemispherical or cushion-shaped, 

 with vents usually arranged in conspicuous groups on the convex upper surface. It 

 attains a considerable size, the largest specimen measuring about 100 millims. in 

 greatest diameter and about 40 millims. in thickness in the middle. 



