43 



direction. Towards the interior, these superficial radial bundles bend round and 

 become longitudinal bundles. Towards the upper, narrow end of the sponge 

 the axial longitudinal bundles approach the surface much more closely, the super- 

 ficial region occupied by the radial bundles thins out, and finally, at the very 

 summit, the longitudinal bundles reach the surface itself. 



As in SemfercUa schuJhel the spicule-bundles of the siipporting-skeleton 

 are chiefly composed of oxypentactiaes. Two of the rays of these spicules lying 

 in one of the axes are very long, two lying in another are a little shorter, and 

 the fifth ray is considerably shorter. To this latter there is either no antagon- 

 istic (sixth) ray at all, or this is represented by a small protuberance only. 



True macrosclere hexactines with six fully-developed rays and true diactines 

 are rare. 



Pentactines also take part in the formation of the oscular sieves which rest 

 on the distal margins of the tube-walls. One ray of these pentactines, which 

 is situated radially, is of considerable length, slender at the base, but thickened 

 in its distal part. The other four rays are very short and terminally rounded ; 

 they form a cross, and extend paratangentially just below the surface (pi. VIII, f . 

 3, 11). Together with these spicules numerous oxypentactine hypodermalia of the 

 usual kind are met with. These have four pretty long paratangential rays, 

 which form a cross, and a radial ray which is generally shorter than the basal 

 rays. All the rays are pointed and often slightly inflated near the end. Such 

 oxypentactine hypodermalia also form the support of the dermal reticulation and 

 the oscular sieve-plate. In these the paratangential rays are elongated and the 

 radial ray much shortened. 



In the stout spicule-bundles of the tube- walls which reach the surface 

 numerous radially-arrai^jged uncinates of the usual form (pi. VIII, f. 7) occur. 

 These are up to 4 mm. long and their distal end generally just reaches the outer 

 surface. 



Occasionally, straight and slender marginalia are met with in the distal ends 

 of the tube-walls which lie just below the surface. These are similar to the 

 marginalia which I found in great numbers in a young specimen of Seviperella 

 schultzei in the " Challenger " collection.* These marginal rhabds are minutely 

 spined and gradually attenuated towards the proximal, pointed end. The distal 

 end is abruptly thickened and bears four pointed spines, arranged crosswise (pi. 

 VIII, f. 10). 



The long bidentate anchor-spicules of the basal root-tuft are on the whole 

 similar to those of SemperelJa schultzei described by previous authors and also })y 

 myself. t They differ from them, however, in the shape of the sharp lateral 



* Cliallenger Eepoi-ts, Hexactiuellida p. 265, pi. LIT, f. 3, 

 + Challeuger Reports, Hexactinellida p. 265, pi. LII, f. 14. 



