TETHTA. 



cortex and the buds alone contain the red pigment. The oseula are circular, 

 2-4 uiillira. ^ide, and very slightly raised above the surface : they are situated 

 on the upper surface of the sponge. There are, according to the size of the 

 specimen, from one to five oseula. 



The sponge is much more dense than the European THhya h/nciinmn. 

 The canals are narrow. In the cortex radially depressed and very irregular 

 lacun©, sometimes 2 miUim. broad and up to 0-4 millim. high, are met with. 

 Also circular canals are found, which have a diameter of 0-4 millim. Both 

 extend tangentially and form subdermal cavities, which are supplied by narrow 

 canals from wdthout. The canals in the pulpa are, with the exception of the 

 exhalant stems, very narrow, on an average 0-064 millim. wide, and disposed 



radially. 



Sl.eieto7i.—A mass of irregularly tangentially disposed spicules forms a solid 

 centre, 2-5 millim. in diameter, which is regularly spherical. From this the 

 0-3-0-5 millim. thick bundles of supporting-spicules radiate, which extend in 

 the cortex in a trumpet-shaped manner, and terminate in the tubercles. The 

 centrifugal ends of the most distal spicules project 0-2-0-3 millim. beyond the 

 surface. The microsclera may be more or less abundant ; but as any number 

 of transition-forms between mnltistellular and paucistellular specimens have 

 been observed by me, I consider these differences as of no systematic import- 

 ance.— (1) 3ferjasclera. Styli 2-3-5 X 0-018 millim., straight, slightly contracted 

 at the rounded end, not very sharply pointed. In the cortex similar smaller 

 spicules are found in connection with the surface-tufts of the radial bundles, 

 which measure 0-5 x 0-006 millim. The pointed end is turned outward and pro- 

 jects beyond the surface.— (2) Stellate Microsclera. These are of two kinds :— 

 (A) With Conical Rays : abundant in the variety TetJu/a multistella megastella, 

 and rare in the variety Tethya multistella microstella ; their rays are conic and 

 sharp-pointed ; they grow out from the central spherical mass, which measures 

 0-012 millim. in diameter, and are 0-01 millim. long and at the base 0-007 

 millim. thick. (B) With Cylindrical Bays, which have a terminal knob : these 

 are small, only 0-01 millim. in diameter, and frequent in the variety microstella. 

 AVith a higher power the terminal knob on the rays can be dissolved into two 

 or more short terminal recurved spines. These spicules are very different from 

 the young stages of the larger stellates, which always have the same shape 

 as the adult spicule, however small they may be. The outer layer of the cortex 

 is composed of these stellates, which form a pretty dense layer in it in the 

 variety microstella. 



Geographical Distetbtjtion.— East coast of Australia: Port Jackson 

 {Ramsay, Lemlenfeld). South coast of Australia : Port Phillip (Lcndevfild). 

 New Zealand, Port Chalmers (Parher) : Chatham Islands (Parl-er). 



