REPORT ON THE TETRACTINELLIDA. 
191 
Spicules. — I. Megascleres. 1. Oxea, 25 mm. in length, possibly as long as the 
cloacal tube, viz., 55 mm. 
2. Orthotrisenes, rhabclome long, lying longitudinally in the wall of the central canal ; 
cladi, two paired and shorter lying horizontally in the wall of the central canal, the third 
unpaired and longer extending radially through walls of adjacent peripheral canals up to 
the dermal membrane. 
3. Modified disenes, rhahdome long, disposed as in the case of the orthotriaenes ; 
cladi unequal in length, one directed like the unpaired cladus of the orthotrisene, the 
other bent upwards, continuing the direction of the rhahdome. 
■4. Triods, these represent the cladome of an orthotrisene, in which the rhahdome has 
entirely disappeared ; the cladi or actines are arranged like the cladi of the orthotrisene. 
II. Microsclere. 5. Spheraster, with numerous short conical actines, 0’007 to 
O'Ol mm, in diameter. These form an almost continuous layer beneath the outer epi- 
thelium. 
Colour. — Chalky-white when dry. 
Habitat. — North New Zealand ; 45 fathoms (expedition of the “ Gazelle ”). 
Remarks. — This species is founded on specimens of the cloacal tube of a Tethyopsis, 
which evidently very closely resembles, if indeed it is not identical with, Tethyopsis 
columnifera, Stewart. The tube differs from that of the latter in being traversed by 
nine instead of four canals ; but this may merely represent a difference in age, for in 
Disyringa dissimilis, Ridley, stages of four, eight, and sixteen canals are known to exist. 
This explanation is consistent with the greater diameter of Marshall’s specimens, 
which measure 55 mm. in length by 15 mm. in width, just twice the width of that in 
Stewart’s specimen. The nine canals of Marshall are possibly reducible to eight, since 
the axial canal may be merely a cleavage fissure. 
In comparing the cloacal tube with that of Disyringa dissimilis in the stage of eight, 
one will observe that the eight canals of the latter are of unequal value, four are primary 
and four secondary, and the latter are nearer the periphery than the former. This is 
not the case in Marshall’s specimens, in which all the eight tubes are of equal value, and 
all radiate from the centre to the circumference. 
There appears to be greater variety in the cloacal megascleres of Tethyopsis radiata 
than in Tethyopsis columnifera ; but this may be explained by the fact that, owing 
to the existence of only a single specimen of the latter, it has not been so completely 
examined. 
Another explanation is also possible. Marshall alludes to the difficulty of obtaining 
preparations of the spicules of the sponge ; and though I think it unlikely, yet I cannot 
avoid making the suggestion that some of the forms figured by Marshall may be fragments 
of orthotrisenes. 
