78 CEYLON PEARL OYSTER REPORT. 



scarcer within ; with numerous rather short, truncate conical rays, and often with a 

 distinct but small centrum ; total diameter about 0'012 millim. or less. 



(4.) Oxyasters (Plate II., fig. 6, i-k) ; fairly numerous in the deeper parts, hut may 

 be difficult to find ; with little or no centrum, and long, slender, conical, sharp-pointed, 

 smooth rays, varying in number ; total diameter about 0'029 millim. 



Owing to the great size and abundance of the megascleres it is impossible to cut 

 satisfactory sections by the ordinary paraffin method, but such as I have been able to 

 obtain have yielded some interesting results. The ectosome is remarkably developed 

 as a very thick gelatinous layer containing numerous stellate ce'lls (collenchyma), and 

 a thin layer of fibrous tissue (about 0'08 millim. thick), situated about 2 '5 millims. 

 beneath the surface and separating the gelatinous layer from the choanosome. The 

 arrangement of the main skeleton appears to be in no way correlated with the 

 differentiation between ectosome and choanosome, the large megascleres passing 

 through the fibrous layer from one to the other without distinction. The mesogloea 

 of the choanosome ranges from collenchymatous to finely granular, and the flagellate 

 chambers are more or less spherical and about 0'024 millim. in diameter. 



There are six specimens of this sponge in the collection. The arrangement of the 

 skeleton reminds one very strongly of SOLLAS'S genus St?*yphnus, but the absence 

 of amphiasters or sanidasters prevents us from placing the species in that genus 

 (according to SOLLAS'S classification). The species also resembles to a considerable 

 extent KIRKPATRICK'S Stelletta (Astrella) horrens, from Sotith Africa (17), but is 

 distinguished by its external form, by the arrangement of the pores and vents, and 

 by the details of spiculation. 



E.N. 66 (Gulf of Manaar) ; 89, 137, 137A, 157, 203 (all from off Galle and onwards 

 up the West Coast, depths up to 100 fathoms). 



Stelletta vestigium, n. sp. Plate II., fig. 7. 



Specimen irregular in shape, massive, encrusting, and containing many calcareous 

 foreign bodies. (In the same mass as the two specimens of Tethya lyncurium 

 var. a.) Maximum diameter about 23 millims. Colour in spirit, nearly black. Vents 

 and pores not seen. No cortex. 



The skeleton is a confused reticulation of megascleres, mingled with foreign bodies 

 and sometimes collected into loose fibres ; with a thin dermal crust of asters, also 

 much mixed with foreign bodies. 



Spicules. (1.) Triaenes (Plate II., fig. 7, a-d) ; with cladi reduced to three, two, or 

 one mere spines or protuberances of varying size at the broad end of the spicule ; the 

 other end tapering gradually to a more or less sharp or irregular apex. These spicules 

 are of about the same dimensions as the oxea. 



(2.) Oxea (Plate II., fig. 7, e) ; rather slender, usually slightly curved; more or 

 less gradually sharp-pointed or irregularly ended ; measuring about 074 millim. by 

 0-016 millim. 



