126 CEYLON PEARL OYSTER REPORT. 



zig-zag, with projections on all sides; length about 0"016 millim., thickness about 

 0'002 millim. (excluding projections) ; (c) long, slender, zig-zag or crooked, with 

 small, sharp spines on all sides; size about 0"048 millim. by (P0027 millim. (excluding 

 spines) ; (d) short, stout, zig-zag, with stout conical spines on all sides ; size about 

 0"022 millim. by 0"004 millim. (excluding spines), with spines about 0"006 millim. 

 long. The spirasters are abundant and form a thin dermal crust. 



The canal system of this sponge is somewhat remarkable and, like the external 

 form, reminds one of Tentorium. The wide exhalant canals, running vertically 

 upwards to the apex of the sponge, have already been noticed. The inhalant pores, 

 situated also at the summit of the sponge, lead into subdermal cavities from which 

 very narrow inhalant canals run vertically downwards, more or less parallel with the 

 oscular tubes. These canals unite together as they descend and, even in hand-cut 

 and unstained sections, can be easily traced by the brown colour of their walls. 



Considering the extraordinary variation which the species of Spirastrella exhibit, 

 alike in external form and in the arrangement of pores and vents, I should hardly 

 have considered characters of this nature alone sufficient to justify the establishment 

 of a new one, but should have regarded this form as yet another variety of 

 Spirastrella vagabunda. We have here, however, a stout form of the spiraster 

 which is, perhaps, not represented in any of the varieties of that species, and this 

 fact, taken in conjunction with the other characters, seems to me to justify a specific 

 separation. 



R.N. 239 (Ceylon seas). 



Placospongia, Gray. 



Spirastrellidse with a stony spicular axis and a similar cortex, both composed of 

 closely packed sterrospiroe ; with bundles of tylostyles radiating from the axis 

 towards the periphery. Cortex divided into polygonal areas by grooves con- 

 taining the inhalant and exhalant apertures. 



Placospongia carinata (Bowerbank). 

 [For Literature and Synonymy, see Vosmaer and Vernhout (35).] 

 In view of the very recent publication of the elaborate monograph on the genus 

 Placospongia, by Vosmaer and Vernhout, it is unnecessary to say much about this 

 interesting species. The presence of numerous parenchymatous spirasters ("spini- 

 spirse"), and the fact that the dermal spicule is a microspire, justify the specific 

 identification according to the views of the authors quoted. I also agree with 

 Keller in placing the genus amongst the Spirastrellidse, it having been shown that 

 the "sterraster" of this sponge is a modified spiraster. 



Carter (4) has described a species of Placospongia from the Gulf of Manaar which 

 he identified as P. melobesioides, and this identification will no doubt hold good, for 

 he expressly mentions the absence of spirasters (" spinispiruke"). He has also (5) 



