Carboniferous of the S.W. of Scotland. 131 
So much for Mr. Thomson’s interesting specimens of 
Hyalonema Smithii. Let us now see what the supply of 
separate spicules by Dr. J. Millar affords. 
1. Fragments of the spicules of the cord.—These vary in 
size from half an inch in length downwards, and the largest 
of the smooth ones 1-24th of an inch in diameter, while the 
largest of those grooved all round the circumference are 
1-244th of an inch thick. There is nothing remarkable 
in the smooth form; but the longitudinal lineation of the 
grooved one may be single or in variable plurality, as 
before stated—that is, confined to one part only (fig. 13, 8), 
or spread more or less equally round the whole circum-~ 
ference of the spicule to the number of thirty-two in a 
spicule possessing a diameter of the thirty-second part of an 
inch (fig. 13, d, e), or may not exceed four at unequal distances 
from each other in a circumference double this size (fig. 13, c). 
Although I have seen the single groove chiefly in the 
smaller spicules, I have only seen the entire circumference 
grooved in the larger ones, with the intervals convex like the 
Jascis of a Roman lictor, not fluted or concave like an Ionic 
column. Whether, however, this grooving, in its extreme 
degree, belongs to the spicules of Hyalonema Smithii or 
not, the more simple one does, as Mr. Thomson’s specimen 
demonstrates in s¢tu ; and reasons have already been assigned 
for its seeming to be original, and not produced by the pres- 
sure of surrounding smaller spicules, whose absence is evi- 
dent where the groove is equally present. Again, although 
the largest spicules I have seen were grooved throughout the 
circumference, it does not follow that the grooved spicules 
are always the largest, as has already been shown. 
2. Fragments with four-armed anchor-like ends.—These 
are of two kinds, viz. :—the larger, with inflated or rounded 
extremity and moderately recurved thick short arms (fig. 5) ; 
and the smaller, with pointed extremity and much recurved, 
longer, and less stout arms (fig. 6). Both kinds have four 
arms opposite. In the former the shaft is slightly reduced 
in size to the point where it expands into the arms (fig. 3), 
or it may be constricted just before this termination, while the 
arms, which in the normal or more regularly formed ones are 
thick conical spines of nearly equal length, and nearly crucial 
or opposite in position, are somewhat recurved (fig. 3, a, 6) ; 
but they may vary in length and obtuseness, in the angle at 
which they separate, and in their degree of recurvation, still 
always parting from an obtuse or rounded club-like extremity. 
This is the character of the anchor end zn situ (fig. 4, a), to 
which I have before alluded; so that we may fairly assign it 
