EEPORT ON THE HEXACTINELLIDA. 73 



united so as to form a tube, which constituted the present connecting bridge and the 

 under extremity of the small tube, while from its upper convex side a new young tube 

 grew upwards. 



Another young specimen, in which the amalgamation of the spicules has not yet 

 commenced, is from 2'5 to 3 cm. broad, possesses a highly arched sieve-plate, and a very 

 well developed system of ridges, together with a completely formed cuff. The ridges have 

 already attained a height of 3 mm. or more. The inferior extremity is unfortunately 

 absent. 



2. Euplectella suberea, Wyville Thomson (PI. V. ; PI. VI. fig. 3). 



Though the Challenger specimens of the new species which W5rville Thomson named 

 Euplectella suberea were not, as a whole, well preserved, the discoverer was still able 

 by combining the various fragments, to obtain so perfect a conception of the size, form, 

 and structure of the whole sponge that he was able to publish, with the help of the 

 artist, the restoration presented in PL V. fig. 1. As is evident indeed from this 

 excellent fio-ure, and from Wyville Thomson's own words, which have been quoted 

 verbatim above on p. 60, the sponge in question is a straight, round, slightly 

 swollen tube, varying from 20 to 25 cm. in length, and measuring about 5 cm. in 

 its greatest breadth. Its walls, it is true, present a general similarity to those of 

 Euplectella aspergillum, but it may be readily distinguished from the latter by the 

 greater regularity of its structure, by the absence of the high external ridges and of the 

 cuff, as well as by the numerous separate projecting radial spicules. 



The parietal gaps lie at a distance of 6 to 8 mm. from one another, within trench-like 

 pits, which are connected by intersecting systems of external, oblique, and spiral furrows, 

 so that the regular spiral arrangement of the parietal apertures becomes all the more 

 manifest. Between every four adjoining parietal gaj)s there is a rhombic area, bounded 

 by the connecting furrows, and provided with a flat, slightly convex, projecting elevation. 



The upper transversely truncated extremity of the tube is bordered by a delicate 

 marginal wreath, from which isolated spicules project upwards and outwards in groups, 

 without forming a continuous fringe. Close beneath the margin there is a wreath 

 of densely placed parietal apertures, while inside the margin a wide-meshed lattice-like 

 network is spread out transversely, the delicate strands of which are arranged partly 

 in a circular, and partly in a radial manner. 



The inferior extremity of the tube, which has become narrowed to about the half 

 of the greatest transverse diameter, is devoid of soft parts, and runs out into an incom- 

 pletely preserved basal tuft of long, thin, siliceous fibres. 



An examination of the inner surface of the wall shows that here, as in Euplectella 

 aspergillum, a quadrate, lattice-like network of longitudinal and circular ridges projects 

 inwards. The meshes are seen to be occupied alternately with a parietal gap, and with a 



(ZOOL. CHALL. EXP. — PAET LIII. — 1886.) Ggg 10 



