REPORT ON THE TETRACTINELLIDA. 
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Family III. Tethyida: (Vosmaer). 
Centrospinthara in which the ectosome is a well-differentiated cortex, with a distinct 
fibrous layer. The megascleres are rhabdi, radially arranged. The microscleres are 
spherasters. 
Genus 1, Tethya, Lamarck. 
Tethyidse of more or less spherical form, in which the rhabdus is a strongyloxea. 
The chamber-system is diplodal. 
Tethya seychellensis (E. P, Wright) (PI, XLIV. figs, 1-6). 
Alemo seychellensis, E. P. Wright, Trans. Roy. Irish Acad., vol. xxviii. (Sci.), p. 13, pi. i., 1881. 
Sponge (PL XLIV. fig. 1). — More or less spherical, attached or free, surface conulose, 
conules gemmiferous, varying in form according to position and the presence, state of 
development, or absence of gemmae. Oscules one or more in number ; pores in sieves, 
situated in the depressions between the conules, leading into extensive intercortical 
cavities (PI. XLIV. fig. 4). 
Spicules. — I. Megasclere. 1. Strongyloxea, fusiform, anisoactinate, esactine strongyl- 
ate, ecactine tapering to a narrower termination than the esactine, but rarely exactly 
oxeate, sometimes tornote, but usually strongylate ; 1’91 by 0'023 mm. (Station, 
Samboangan), 1’68 by 0‘026 mm. (Station 186). 
II. Microscleres. 2. Cortical spheraster, centrum large, actines conical, oxeate, 
usually from twenty to twenty-four in number, 0'095 mm. (Station, Samboangan), 0'064 
mm. (Station 186) in diameter. 
3. Somal chiaster, centrum variable, sometimes abseut, sometimes well marked ; 
actines cylindrical, varying in length, diameter, and number, terminally tylote ; 
0’0118 mm. in diameter. 
4. Choanosomal aster, very variable, actines slender, straight or curved, conical, oxeate, 
irregularly spined, or cladose, dichotomising irregularly, once or oftener ; the length of a 
single actine 0 ‘02 76 mm. ; centrum small or absent. 
Colour. — Greyish-white in spirits; on upper surface light ruddy-brown (E. P. W.). 
Habitat. — Station 186, Flinders Passage, September 18, 1874; lat. 10° 30' S., 
long. 142° 18' E. ; depth, 8 fathoms; bottom, coral mud. Dredged. 
Samboangan. 
South-east of Mahe, Seychelles Islands, inner margin of a coral reef; August 1867 
(E. P. W.). 
