80 
THE VOYAHE OF H.M.S. CHALLENGER. 
at its edge, radiately arranged with respect to the spire ; the length of the spicule does 
not exceed 0‘02 mm., of a single spine 0'004 mm. 
Colour. — White, with a faintly yellowish tint. 
Habitat. — Station 150, Heard Island, February 2, 1874 ; lat. 52° 4' S., long. 
71° 22' E.; depth, 150 fathoms; bottom, coarse gravel; bottom temperature, 35°'2. 
Remarks. — This species is readily distinguished from PcEcillastra {Normania) crassa, 
Bwk., by the dimensions of its spicules and the characters of its canal system. The fusi- 
form oxea (1) and the trisene (3) have twice the length and breadth of the corresponding 
spicules in Pcecillastra crassa ; and the oscules are small, numerous, evenly dispersed, 
while in Pcecillastra crassa there are several somewhat large oscules congregated 
together. Two complete specimens and fragments of a very large one occur in the 
collection. Of the complete specimens, the larger is represented on PI. IX. fig. 1. It 
measures 100 mm. in height, 85 mm. in breadth, and is 9 mm. thick. The other and 
smaller one is more irregular in form ; a somewhat fan-shaped plate, irregularly undulating, 
raised in places into irregular ridges, and with sinuous margins. It measures 42 mm. in 
height, 53 mm. in width, and 4 to 5 mm. in thickness. The fragments consist of several 
plate-like pieces, and one in which a plate-like wall has grown from a linear attached base 
into a wide tube of an oval section, 72 by 43 mm. in diameter. It appears to form the 
basal part of a cup, of which the remaining pieces helped to form the wall ; part of the 
sponge, however, has been lost, as I could not build the pieces together into a complete 
form. From the reconstruction I effected, the whole sponge would appear to have been 
a vase at least 160 mm. high, and 160 mm. broad. The wall is about 8 mm. in thickness. 
The pores, 0'09 to OT mm. wide, occur several together in oval groups, each group forming 
a fenestrated membrane, v\rhich roofs over a circumscribed subdermal cavity — in other 
words, the origin of an incurrent canal ; this is broken up below by numerous partitions 
of collenchyme, coated by epithelium, into several smaller incurrent canals. The oscules 
occur as single apertures, 0T6 to 0'318 mm. in diameter, in the centre of a membrane 
which roofs over the ends of cavities in the ectosome in which the excurrent canals 
terminate. This and the poriferous membrane are supported by oxeate spicules lying 
tangentially, and by the extended arms of the trisenes, the rhabdomes of which descend 
through the ectosomal pillars. Beneath the epithelium of these membranes is a layer of 
thickly evenly dispersed spirasters, which extend up to the margin of the pores and 
oscules, their spines projecting beyond. Beneath these, again, microxeas occur, which 
tangentially surround the margins of the oscules and the poriferous areas, but do not 
extend to the extreme edge. The subdermal cavities of the incurrent face are irregular, 
winding, branching canals, from which the incurrent canals take their origin, extending 
transversely through the sponge-plate in the opposite direction to that of the excurrent 
canals, which extend inwards from the oscules. The course of both sets of canals, though 
