130 Mr. H. J. Carter on Sponges from the 
posed by the fracture of the limestone in which it lies im- 
bedded, it does not exceed in the thickest part more than one 
sixth of an inch, as before stated (fig. 2). 
In the smallest of the three specimens, which is not more 
than an inch long and in which the spicules are much reduced 
in size and spread out, indicative of the free end of such a 
cord, is an instance of the terminal or anchoring extremity in 
situ, presenting the same inflated, club-like form we shall find 
hereafter to be so common among the separate fragments, but 
with the shaft at its junction with the anchor-like end only 
1-120th inch in diameter (fig. 4, a). 
It is not uncommon, as we shall presently see, to find the 
cord-spicule grooved longitudinally, in one part singly, or 
generally and in great plurality throughout its circumference 
(fig. 13, 6, d,e), which has been attributed by the Messrs. 
Young to pressure from the “adjacent rods” (J. c. p. 427) ; 
but on examining the end of one of Mr. Thomson’s speci- 
mens with the microscope, two rather large spicules may be 
seen close together with a single groove in each, and the material 
between them and the neighbouring spicules entirely composed 
of the white granular calcite which fills up the intervals be- 
tween these spicules, and thus, in the transverse section, 
contrasts strongly with the dark end of the transparent mate- 
rial of which the spicule is formed, without the presence of 
any small spicules whatever (fig. 13, aa); so that this groov- 
ing would appear to be original and not Sout by “ adja- 
cent rods.” Besides, where there are small spicules in distinct 
contact with larger ones, there is no groove at all observed in 
the latter, which therefore may be natural although of casual 
occurrence. 
The fragments of the surface of the body of a sarcohexac- 
tinellid sponge, attributed to Hyalonema Smithii, were also 
sent tome by Mr. Thomson, in which the characteristic spicu- 
lation of the surface in this species is obvious together with 
the lattice-like structure formed by the intercrossing of the 
spicules in the Sarcohexactinellida generally. The largest of 
these pieces is about half an inch long by a quarter of an inch 
broad (fig. 7), in which there is one of the circular fenestral 
spaces (now a hole) forming the interstices of the lattice-like 
structure, also characteristic of the recent Sarcohexactinellida, 
together with remains of others on the circumference (fig.7, bd), 
and the peculiar “ nail-like”’ spicules described by Dr. Young 
(l.c. p. 426) of all sizes below 1-6th of an inch in diameter 
across the head, which is possessed by the few that chiefly 
bind down the rest with sloping outspread arms, after the 
manner of this kind of spicules generally (fig. 7, a a). 
