TETHYA. 



61 



Skeleton.— (1) Monad Megasdera. The radial bundles 0-3 millim. thick, are 

 composed of styli which measure 2 x 0-018 millim. and which are straight and 

 cylindrical ; the pointed end looks outward ; the distal spicules of the bundles 

 project slightly beyond the surface. Similar spicules, measuring 1x0-008 

 millim., surround the surface-tufts, pointing obliquely outward; it is always 

 the pointed end which projects.— (2) Stellate Microsdera. Three varieties of 

 stellates occur in this species :— (A) Large, spherical spicules, with conic rays, 

 measuring 0-06 millim. in diameter, and forming a dense mass in the cortex ; 

 the same spicule is also found in abundance in the interior of the sponge. (B) 

 Small stellates, with slender cylindrical rays, which are terminally thickened ; 

 these stellates measure 0-006 millim. in diameter, and are not found on the 

 outer surface ; in the cortex they are rare, but more abundant in the pulpa. 

 (C) A stellate spicule found in the pulpa, which is peculiar to this species ; 

 it is about as frequent as the foregoing variety. This stellate has no visible 

 central body and it has slender conic rays, which are covered with long 

 spines ; these spicules measure 0-03 millim. in diameter, each ray is 0-014 

 millim. long, and at the base 0-003 millim. thick. 



Geoqeaphical Distribution.— South coast of Australia : Port Phillip, V. 

 (Lendenfeld). 



Tethya Isevis, n. sp. 



Spherical or oval sponges, attaining a diameter of 20-50 millim., attached by a 

 small base,2-6 slit-shaped oscula on the upperside, which measure 1 x 0-2 millim. 

 in diameter ; thread-shaped appendages, which may attain a length of 20 and a 

 thickness of 2 millim., are found either in groups or appear scattered irregularly 

 over the surface. The surface is smooth or slightly tubercular ; often one por- 

 tion of the surface is smooth and the other tubercular. In spirit light brown on 

 the outer surface and in the interior ; the lower layer of the cortex appears 

 white. The smaU inhalants join to form stems, which traverse the cortex in 

 a centripetal direction, and have a diameter of 0-1 millim. Irregularly reticu- 

 lating canals, which pervade the cortex in every direction, connect the vertical 

 canals with each other. The canals in the interior are not so regularly radial 

 as in other species of this genus. 



SJceleton.— The centre from which the bundles radiate is situated in the middle 

 of the sponge ; the radiating bundles have a thickness of 0-8 millim. ; they divide 

 iu the cortex into several branches, and expand so much that no space is left 

 between the surface-tufts. Stellate spicules are found in the cortex and pulpa. 

 —(1) Megasdera. Styli 2 x 0-1 millim., cylindrical, sharp-pointed, sometimes 

 very short, only 0-6 millim. long, pointed end always centrifugal. There are 

 no smaller cortical monaet spicules around the suface-tufts, as in the other 

 species.— (2) Stellate Spicules. Of three kinds :-( A) Large spherical spicules. 



