116 CEYLON PEARL OYSTER REPORT 



Xenospongla patelliformis, GRAY Plate VI. 



1858, Xenospongia patelliformis, GRAY (30); 1867, Xenospongia patelliformis, GRAY (31); 

 1873, Xenospongia patelliformis, HOI.DSVORTH (9); 1875, Xenospongia patelliformis, 

 CARTER (32) ; 1882, Xenospongia patelliformis, CARTER (33) ; 1888, Xenospongia 

 patelliformis, SOU.AS (15) ; 1898, Xenospongia patelliformis, TOPSENT (26). 



The single specimen in the collection (Plate VI., fig. 1) has the form of an almost 

 circular disk, about 28 millims. in diameter, with convex upper and slightly concave 

 lower surface and rather thin and slightly undulating margin. The lower surface is 

 formed by the agglutinated sand which makes up the greater part of the thickness of 

 the disk. The upper surface is covered with rather small, rounded tubercles or 

 conuli, thickly scattered at fairly regular intervals. These tubercles are about 

 1 millim. in diameter, and are normally hispid from the projection of the ends of 

 large spicules, now generally broken off short. The margin of the sponge is also 

 very shortly hispid from the same cause (figs. 1, 2, m.f.). Just above the margin 

 two narrow grooves (figs. 1, 2, m.p.g.) run round the disk, separated from one another 

 by an interval of about 1'5 millim., across which they occasionally communicate with 

 one another by oblique connecting grooves. The width of the grooves varies up to 

 about 0'5 millim., and the floor is crossed at right angles by narrow parallel bands of 

 fibrous tissue of a whitish appearance, arranged very regularly at short intervals. 

 The inhalant pores are very minute and arranged in transverse rows between the 

 fibrous bands in the floor of the grooves (fig. 2). (In the specimens described by 

 GRAY similar grooves radiate more or less abundantly from near the centre of the 

 disk towards the margin ; in our specimen these radiating grooves are very feebly 

 developed and recognizable in only a few places, fig, 1, r.p.g.) The vents, now 

 more or less closed, are situated at the apices of three low, monticular elevations 

 near the centre of the disk (figs. 1, 2, o) ; these elevations are not very conspicuous 

 and are apparently formed each by the agglomeration of three or four of the surface 

 conuli.* (Dr. GRAY appears to have mistaken the inhalant pores, or groups of pores, 

 for vents ; some of the prominent elevations figured by him on his larger specimen 

 probably bear the true vents, though one, at least, of these elevations appears to 

 contain a parasitic barnacle ; there appear to be no barnacles in our specimen, but a 

 parasitic worm occupied one of the larger exhalant canals.) 



The colour of the sponge on the upper surface (in spirit) is pale yellowish grey, witli 

 a faint pinkish tinge in places, reminding one much of Tethya. The texture is firm 

 and compact, leathery above, but the greater part of the thickness of the disk is 

 composed almost entirely of coarse sand (fig. 2, s.g.), firmly cemented together by the 

 tissues of the sponge. This sand is exposed only on the lower surface. The total 

 thickness of the disk in the middle is about 6 millims. 



The main skeleton consists in the lower two-thirds of the thickness of the disk, or 



* In addition to the vent-bearing elevations, there is one larger, wart-like protuberance containing some 

 hard foreign body (fig. 1, a). 



