68 CEYLON PEARL OYSTER REPORT. 



of the sponge and sometimes projecting beyond the surface. Vents small and few, on 

 rounded ends of branches. Pores scattered in irregular groups ; many in each group, 

 easily visible under a pocket lens. Colour in spirit, greyish brown. Total height, 

 20 millims. ; greatest breadth, 26 millims. 



The skeleton is for the most part very confused. The choanosome is densely 

 strewn with large oxea lying in every direction and occasionally aggregated in loose 

 bundles ; with these are mingled oxea of smaller size and a few tetract spicules, 

 while the interspaces are filled in with immense numbers of oxyasters, uniformly and 

 thickly scattered through the soft tissues. On the surface of the sponge is a dense 

 layer of small oxea, tangentially disposed, and for the most part lying so close 

 together as to touch one another and form a continuous crust, perforated by the 

 numerous circular inhalant pores where these occur. Beneath this dermal crust are 

 extended horizontally a number of the large oxea and the heads of the dichotrisenes. 



Spicules. (1.) Dichotrisenes (Plate II., fig. 2, a-d), with cladi extended beneath 

 the dermal crust and shaft projecting inwards at right angles to the surface. The 

 shaft is short, stout, and fairly gradually sharp-pointed, only about as long as the 

 radius of the cladome (or even shorter), measuring, say, about 0'37 millim. by 0'055 

 millim. The protocladi are short and stout, about 0'092 millim. by 0'055 millim. The 

 deuterocladi are about two and a half times as long as the protocladi, but variable ; 

 fairly gradually and sharply pointed, commonly slightly curved and often unequal. 

 Boiled-out preparations show various monstrous forms of this spicule, e.g., one with 

 one cladus unbranched, another with one deuterocladus itself branched, another with 

 the shaft branched, and also a number of very much slenderer forms of the same spicule 

 which are probably not fully developed. Although these dichotrisenes are essentially 

 characteristic of the sub-dermal skeleton, yet we find a good many branching spicules 

 scattered through the deeper parts of the sponge, which evidently belong to the same 

 type. 



(2.) Oxea (Plate II., fig. 2, e-p). a, large ; more or less curved or even angulated 

 in the middle ; fusiform ; usually gradually and fairly sharply pointed ; size about 

 1'2 millims. by 0'037 millim. Occasionally a slightly curved stylote spicule may be 

 observed, with one end broadly rounded ; apparently derived from an oxeote by 

 suppression of one ray. b, small ; found chiefly in the dermal crust ; fusiform, 

 gradually and sharply pointed, slightly curved ; varying very much in size ; 

 averaging, say, about 0'18 millim. by O'Ol millim., but ranging from about a third of 

 these dimensions through intermediate sizes to the large forms. 



(3.) Rather large oxyasters (Plate II., fig. 2, q-v), abundantly strewn through the 

 choanosome : with usually about five long, slender and gradually sharp-pointed rays, 

 which are smooth and up to about 0'025 millim. in length ; there is no centrum. 



Stained sections show that the ectosome is rather thin, apparently consisting only 

 of the dense spicular crust and with no fibrous tissue except a little around the 

 oscular tubes. The choanosome is gelatinous (collenchymatous). Both ectosome and 



