A FRESH WATER SPONGE FROM SABLE ISLAND.—MACKAY. 321] 
ranging from 1.5 to £ microns thick: the rotules being plane 
disks less than % microns thick from the point where the shaft 
begins to swell into them. and from 10 to 16 microns in diameter, 
commonly near 12 microns, laciniately blunt-lobed around their 
margins, the shaft occasionally extending 1 micron beyond the 
disks, making the exterior of the rotule slightly umbonate. 
Long birotules: From 35 to 50 microns. commonly from 40) 
to 45, with usually a smooth, uniform shaft about 2% microns 
thick ; the rotules generally of 3, to 4or 5 rays which are slightly 
incurved, the rotule ranging from 8 to 14 mierons in diameter, 
commonly from 10 to 11 microns. 
Larger skeleton spicules : Shghtly curved, microspined or 
rough, tapering gradually from the middle, then more rapidly 
towards the ends; ranging from 150 to 260 microns in length, 
commonly from 180 to 220; and from 3.5 to 5 microns in 
breadth at the thickest part. 
Intermediate skeleton spicules: Generally smooth, and from 
2 to 8 microns thick, and from 150 to 200 microns in length, 
numerous and generally fascicled into strands which are often 
connected transversely by the larger spicules. 
Smaller strand spicules and filament strands - Finer strands 
than those referred to above, appearing as if made up of continu- 
ous filaments instead of spicules; strands commonly from 10 to 
15 microns across, made up of about 20 filaments or more, each 
about one micron thick, where broker. across appearing as if 
they were flexible to some extent, the ends of the filaments 
showing a more or less distinct curvature. Under the micro- 
scope they appear identical with the more slender spicules with 
the exception that they appear to be continuous in the strand. 
Examined with polarized light they are visible in the dark field, 
as are also, more or less, the strands made up of the interme- 
diate spicules while the spicules are cemented together, suggest- 
ing a peculiar colloidal siliceous or a spongin cement. When 
heated with nitric acid these filaments appear first to separate 
and break into pieces, then partly at least to disappear. At the 
earliest opportunity I purpose to examine the nature of these 
Proc. & Trans. N. S. Inst. SCL ViOle ox TRANS.—U. 
