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THE VOYAGE OF H.M.S. CHALLENGEK. 
Order II. LITHISTIDA, 0. Schmidt. 
Tetractinellida provided with a consistent skeleton by the zygosis of modified spicules 
or desmas. 
Suborder I. HOPLOPHOEA. 
Lithistida provided with special ectosomal spicules, and usually with some form of 
microsclere. 
Demus I. Triainosa. 
Hoplophora in which the ectosomal spicules are some form of trisene, and in which 
microscleres (spirasters, amphiasters, or microrabds) are invariably present. 
Family I. Teteacladida: (Zittel). 
Trisenosa in which the desma is tetracrepid. 
Genus 1. Theonella, Gray. 
Tetracladidse with a large single oscule, the external opening of an axial cloaca, or 
with numerous oscules dispersed on the interior surface of a cup-shaped sponge ; pores 
in sieves, generally distributed over the exterior. The ectosomal megasclere is a 
phyllotrisene ; discotrisenes are absent. The microsclere is a microstrongyle. 
Theonella swinhoei, Gray (Pis. XXIX., XXX.). 
Theonella siuinlioei, Gray, Proc. Zool. Soc. Pond., pp. 565, 566, woodcut, 1868. 
„ „ Carter, Ann. and Mag. l^at. Hist., ser. 4, vol. xii. p. 437, 1873. 
„ „ Zittel, Abhandl. d. k. baier. Akad. d. Wiss., Bd. i. pp. 103, 151, pi. i. fig. 9, 
1878. 
„ ,, Carter, Ann. and Mag. Nat. Hist., ser. 5, vol. vi. p. 147, 1884. 
Sponge (PI. XXIX. figs. 1-3). — Simple, erect, attached, more or less cylindrical, with 
a smooth surface, raised into unequal irregular bosses and high, sinuous, longitudinal 
and transverse, anastomosing ridges. The single circular oscule is situated in the centre 
of the rounded summit, surrounded by a smooth wrinkled membrane. It leads into a 
cylindrical cloaca, which extends axially through nearly the whole length of the sponge, 
and is lined by a network of collenchyma, limited by a smooth shining concentri- 
cally ridged or plicated membrane, fenestrated by a multitude of small oval apertures, 
and perforated by larger openings, which lead into the main branches of the cloaca. 
