132 Mr. H. J. Carter on Sponges from the 
to Hyalonema Smithii. How far the other form, which, in its 
largest examples, is not much smaller than the club-shaped 
end, belonged also to H. Smithiz, I am not prepared to state ; 
but although some of its largest examples may surpass in size 
the smallest club-shaped ones, the smallest of the former that 
has come under my observation does not exceed the 1-360th 
part of an inch in diameter, and is therefore microscopic, while 
the largest club-shaped anchoring end reaches 1-16th of an 
inch, and the smallest that I have seen is still visible to the 
unassisted eye. Where the shaft is constricted close to the 
end, the arms are also constricted respectively, so that there 
is no club-like or rounded extremity, so far as my observation 
extends, but in its place a crucial depression ; hence this is 
either a variety of the club-shaped anchor end or the anchoring 
end of a spicule which belonged to another hexactinellid 
sponge. 
3. Fragments of the “ nail-like” spicule—One of these, 
viz. the “ nail-like”’ spicule of (?) Hyalonema Smithit,is smooth 
throughout and consists normally of a shaft with four arms, 
more or less opposite each other, surmounted by a round head 
(figs. 8,9). In size the largest measure about 4-12ths inch 
across the arms, each arm, which is sharp-pointed, being about 
2-12ths inch long, with a thickness at the base of about 1-48th 
inch; the shaft is about the same, or perhaps a little less, and 
the round or globular head, which represents a continuation of 
the shaft, about 1-36th inch in diameter. But all these mea- 
surements, as well as the spicules themselves, are subject to 
great variety, inasmuch as the arms, individually or collectively, 
may be more or less inclined towards the shaft, and thus not 
all at the same angle; or they may depart from the shaft at 
different angles laterally and thus be not opposite; while, in 
form, one or more may vary from an obtuse point to a short 
round knob like the head, or be constricted where they join 
the shaft (fig. 9) ; while the shaft, which is in a line with the 
head, varies very little in shape (like the globular head), being 
for the most part straight and pointed, although sometimes 
both head and shaft, individually or collectively, like the arms, 
may be more or less constricted at the base. ‘The position of 
these spicules in the sponge is illustrated by Mr. Thomson’s 
fragment (fig. 7,aa), where the shaft is directed inwards, the 
head or knob externally, and the arms spreading out laterally 
slope inwardly, so as in the largest forms to bind down the 
rest of the structure as in the Sarcohexactinellida generally, all 
of which, even to the minutest spicule observable on the 
surface, present the same characteristic head and figure as 
that above described with its modifications. 
