128 CEYLON PEARL OYSTER REPORT. 



the outer ends of very loose, irregular wisps of styli which come oif from the dense 

 central portion of the main skeleton. 



Spicules. (1.) Styli (Plate V., fig. 8, a, b, c) ; rather long and rather slender, 

 subfusiform, with the base rather narrower than the middle and the apex fairly 

 gradually sharp-pointed ; usually slightly curved ; size about 0"54 millim. by 

 0-012 millim., but variable. The apices have a tendency to be irregular and 

 occasionally the spicule becomes oxeote. 



(2.) Sanidasters (Plate V., fig. 8, d) ; each in the form of a very slender rod, 

 straight or slightly crooked, terminating at each end in a slight swelling or, perhaps, 

 a couple of small spines, and bearing very slender spines along its length, usually 

 most strongly developed in, or perhaps even confined to, a whorl on each side of the 

 middle of the spicule. Total length about 0'012 millim. ; maximum diameter, 

 including spines, about 0'004 millim. These spicules appear to be almost, if not 

 quite, confined to the dermal membrane on the outer surface of the sponge. 



RN. 362 (Stat. I., hauls 1-4, January 31, 1902, off Negombo, 12 to 20 fathoms). 



Family: CLIONID^. 



Astromonaxonellida of boring habit ; forming excavations in the shells of Mollusca 

 and other calcareous bodies. 



Cliona, Grant. 



Clionidse of which the complete spiculation is composed of tylostyli, oxea, and 

 spirasters. One. or two of these forms of spicule may be absent by atrophy. 

 It will be seen that I have adopted Topsent's views (36, 37) as to this genus and 

 its systematic position, in preference to those expressed in the Eeport on the 

 " Challenger " Monaxonida. 



Cliona margaritiferae, n. sp. Plate V., fig. 9. 



The specimens in the collection consist of pieces of the shell of Margaritifera 

 vulgaris (the Ceylon Pearl Oyster), abundantly excavated by the sponge. The 

 chambers which it makes are rounded or oval in form, more or less crowded together, 

 according to age, and connected with one another by narrow tunnels. From the 

 inner sides of the chambers slender, elongated, conical canals radiate at various angles 

 towards the inner surfiice of the shell. These outgrowths are shaped like spines, and, 

 as in certain other species which I shall refer to later on, give the chambers a very 

 characteristic appearance when viewed by transmitted light. From the outer side 

 of each chamber are given off usually about two cylindrical canals, which perforate 

 the outer layer of the shell at right angles to the surface and terminate in circular 

 vents or pore-areas (fig. 2, on p. 144, shows a shell excavated by this sponge). 



