cxxviii 
THE VOYAGE OF H.M.S. CHALLENGER, 
The Pachastrellidse cannot, however, be included in the same family (as the higher 
Tetillidse are with the lower), because they afford a new point of departure for fresh 
modifications of the microscleres, as is illustrated in the difference between these spicules 
in Dercitus and Pachastrella. 
The Theneidse are evidently an annectant group, uniting the Pachastrellidae and the 
Stellettidse with the Tetillidse. 
Genus 1. Thenea, Gray. 
Thenea, Gray, Proc. Zool. Soc. Lond., p. 541, 1867. 
„ SoUas, Ann. and Mag. Nat. Hist., ser. 5, vol. ix. p. 429, 1882. 
„ Vosmaer, Niederl. Archiv f. Zool., Suppl.-Bd. p. 5, 1882. 
History. — A full account of the history of this genus appears in my Report of the 
Sponges collected by the Rev. Dr. Norman from Kors Fjord, Norway {loc. cit. supra). 
It will therefore not be necessary to give more than a short summary here. The name 
Thenea was first proposed by Gray {loc. cit.) to include Tethya muricata, Bowerbank,^ 
Subsequently various authors described other specimens of this Sponge without recognising 
their identity with it or with each other, and so bestowed new names upon them ; thus we 
have Tisiphonia, proposed by Wy^dlle Thomson,^ Wyville-ihomsonia, by Perceval Wright,^ 
and Dorvillia, by Saville Kent.^ After the resuscitation of the name Thenea, which it 
should be mentioned had been already recommended by Perceval Wright, a paper appeared 
by Vosmaer in which its adoption was also advocated {loc. cit. supra), and it may now be 
taken as definitely established; Carter,® who was inclined to another view, at length 
giving in his adherence. 
Definition . — Theneidae of symmetrical form, with one or more well-defined oscules, 
and specialised poriferous areas, in addition to pores generally distributed. The 
distinctive spicules are dichotriaenes, which together with the other megascleres are 
radially arranged. 
The species of Thenea are usually agariciform, and either radiately or bilaterally 
symmetrical, in the radiate forms an upper moiety is usually separated from a lower by a 
special poriferous recess, which is equatorial in position and either continuous or broken 
up into a series of more or less oval areas ; the upper moiety or “ pileus ” bears the oscule, 
or oscules, and ends in a sharp “ tegminal ” edge, often continued into a fringe of spicules, 
overhanging the poriferous recess ; in bilaterally symmetrical forms, from which all trace 
of radiate symmetry has disappeared, the distinction into a pileus and basal portion fails 
^ Bowerbank, Proc. Zool. Soc. Lond., p. 115, 1872 ; Mon. Brit. Spong., vol. i. pp. 25, 108, 1864; see also p. 95 of 
descriptive part of this Report. 
2 Wyville Thomson, Phil. Trans., p. 712, 1869. 
2 E. P. Wright, Quart. Journ. Micr. Sci., vol. x. p. 7, pi. ii., 1870. 
* Saville Kent, Monthly Micr. Jowrn., p. 293, pi. Ixvi., 1870. 
® Carter, Ann. and Mag. Nat, Hist,, ser. 5, vol. xi. pp. 354, 362, 1883. 
