SPONGES. 1 |:i 



regard them as belonging to three varieties of the well-known and extremely variable 

 Tethya lyncurium of European waters. For convenience of reference we may dis- 

 tinguish the Ceylon varieties as a, b, and c respectively. . 



Tethya lyncurium, Lin., var. a. 



This variety is represented by two approximately spherical specimens growing side 

 by side on a mass of calcareous and other debris. The larger of the two is about 

 20 millims. in diameter, the other only a little less. The colour in spirit is dull 

 yellowish-grey. The surface is irregularly conulose and gemmiparous, not distinctly 

 tessellated, and to a considerable extent covered by adherent foreign matter. Each 

 has a single prominent and widely open vent, about 2 millims. in diameter, at the 

 summit of a thin-walled tubular projection. The pore-sieves between the conuli are 

 for the most part inconspicuous. 



The cortex is very dense and more or less fibrous throughout, but the fibrous tissue 

 is most strongly developed in its deeper portion. The inhalant canals in the cortex- 

 are lacunar near the surface and constricted into definite canals deeper down. 



The main skeleton consists of stout radiating bundles of megascleres, breaking up 

 into divergent brushes in the cortex. In the choanosome (but not in the cortex) 

 loose spicules of similar form are abundantly scattered (mostly lengthwise) between 

 the bundles. 



The megascleres are rather slender, faintly tylote styli, of the ordinary Tethya 

 form. The feebly developed bead is narrower than the middle of the shaft, and the 

 apex is gradually and more or less sharply pointed. These spicules measure about 

 t - :l millims. by 0"02 millim. in the main fibres, but are much smaller in the surface 

 brushes, while between the main fibres, in the choanosome, the sizes are mixed. 



The microscleres are of two forms only, spherasters and chiasters. The spherasters 

 are mostly found in the cortex, where they are rather sparingly scattered. The 

 centrum is fairly large, and they have sharp-pointed conical rays which may be 

 (rarely) spined or branched. The rays are about 12 in number, and nearly or quite 

 touch one another at their bases. Total diameter about 0"076 millim., with rays 

 0'02 millim. lono-. In the cortex the chiasters are most abundant at the surface and 

 in the walls of the inhalant canals ; they are also numerous in the choanosome. They 

 have no centrum and about from 6 to 9 distinctly tylote, rather slender rays. The 

 total diameter of the chiaster is about - 012 millim. Those of the choanosome are 

 commonly six- rayed, and the rays are occasionally more elongated and i^oportionately 

 more slender than in the ordinary form, but they are almost always distinctly tylote, 

 and the whole spicule is never more than about - 02 millim. in diameter. 



I am convinced that the two specimens described above cannot be distinguished 

 more than varietally from the common European species. The chiasters are, it is 

 true, more distinctly tylote than is usually the case in T. lyncurium, but I cannot 

 regard this character as of specific value, for in a specimen from Budleigh Salterton, 



