146 
THE VOYAGE OF H.M.S. CHALLENGER. 
Colour . — Gr eenish'grey . 
Habitat . — Station 161, off Melbourne, April 1, 1874; lat. 38° 22' 30" S., long. 144° 
36' 30" E. ; depth, 33 fathoms ; bottom, sand. Trawled. 
Remarhs. — The ectosome (PI. XIII. figs. 39, 40) is about 0‘4 mm. in total thick- 
ness ; the pores open directly into mde canals, which terminate below by freely opening 
into extensive subdermal cavities, from which the incurrent canals are produced inwards. 
These, like the excurrent canals, are widely open, crossed by vela with wide apertures, 
and surrounded by thin collenchymatous walls, in which fusiform and vesicular cells 
occur as we, 11 as collencytes. The ectosome, owing to the extensive subdermal cavities, 
is reduced chiefly to an outer layer, 0T3 mm. thick, forming the roof of these cavities, 
and to the pillars of tissue between them ; the floor of the subdermal cavities is only 
separated from the choanosome by the epithelial lining and a discontinuous layer of vesicular 
cells, not more than O' 00 8 mm. in diameter. The ectosomal tissue forming the roof of 
the subdermal cavities consists of collenchyma, in which are abundance of fusiform cells, 
especially numerous immediately below the dermal epithelium ; they lie tangentially, 
except in the pillars between the subdermal cavities, where they assume a radial direction. 
Just below the margin of the pores, directed at right angles to the surface of the poral 
canal, small, deeply stained, fusiform cells are in some cases conspicuously present ; they 
are about 0'024 mm. long, it may be a little longer, and the nucleus is situated about 
O' 00 9 mm. from the outer end, which is in immediate contact with the lining epithelium 
of the canal, if indeed it does not penetrate it (PI. XL. figs. 1, 2), In form, general 
characters, direction, and position these cells are strikingly similar to those which von 
Lendenfeld has interpreted as sense-cells. 
The choanosome is a sarcenchyma. The flagellated chambers are about 0'03 by 
0'024 mm, in length and breadth, the choanocytes 0'012 mm. in length, with a spherical 
body about 0'004 mm. in diameter; the collum can be traced as a double contoured 
band up to its entrance into the fenestrated membrane. The apopyle and prosopyle are 
of about the same diameter, from 0'008 to O'OIS mm. 
Anthastra pyriformis, Sollas (PI. XV. figs 1-19). 
Ecionema pyri.formis, Sollas, Prelim. Account, Sci. Proc. Roy. Hubl. Soc., vol. v. p. 192, 1886. 
Sponge (PI. XV. figs, 1, 2) somewhat obconic, attached by a flattened base, rising by 
straight sides, which pass by a gently rounded margin into a flattened or depressed upper 
surface, bearing numerous small oscules. Chief excurrent canals vertically ascending to 
open each by one or more chones in the oscules. Pores large, in sieves, generally dis- 
tributed over the sides. 
Spicules. — I. Megascleres. 1. Oxea (PI. XV, fig. 3), massive, fusiform, sharply 
