134 Mr. H. J. Carter on Sponges from the 
Thus the largest of all these three kinds of “ nail-like” 
spicules appear to have been about the same size, and the 
three different forms to have belonged to three different sarco- 
hexactinellids respectively, while the first only has been seen 
in situ; so that each of these three kinds may have been the 
nail-like body-spicule of a particular species. At the same 
time it should be remembered that, although the “ nail-like” 
spicule first described has been found zn sztw in the body- 
structure of the sarcohexactinellid to which it belonged, this 
body-structure has not as yet been found in direct connexion 
with the cord, and therefore has only been assumed to have 
been part of Hyalonema Smithii from its association with the 
fossil cords; while the only instance of an anchoring termi- 
nation like that assigned to H. Smithiz that has been found in 
direct connexion with the fragment of a cord is that above 
mentioned. Again, according to the Messrs. Young’s state- 
ment (/. c. p. 428), the cords are so abundant that it may be 
fairly inferred that they did not ad/ belong to the same species 
of hexactinellid. 
The double sagittate form of anchor end, also above men- 
tioned (Pl. IX. fig. 6), may have belonged to one of the species 
in particular; while the four arms opposite with their varieties, 
in the cord as well as in the nail-like body-spicule, seem 
to indicate an alliance with the genus ossella rather than 
with Hyalonema (‘ Ann.’ 1872, vol. ix. pl. xxi.). At the 
same time the Messrs. Young’s statement that “the rods 
are of unknown length, the largest fragments at Trearne being 
12 inches, and of various thicknesses, from 1-40th inch to 
nearly a line in diameter,” shows that they far exceed in 
dimensions those of the largest specimens of any Hyalonema 
that I have seen, and dwarfs to almost insignificance the 
longest of Rossella, which are only 6 inches with a corre- 
sponding thinness (‘ Ann.’ 1875, vol. xv. p. 19, pl. x.), while 
the anchoring ends of the cord-spicules in the largest recent 
Hyalonemata can hardly be seen with the unassisted eye, being 
not more than 1-140th inch in diameter. 
Replacement of siliceous by calcareous material during 
fosstlization. 
Connected with the fossilized spicules of Hyalonema Smithit 
is the fact that many of the fragmentary spicules sent to 
Dr. Millar by Mr. Armstrong, and obtained, as before stated, 
from the ‘rotten material”? or decomposed limestone, re- 
spectively present all degrees of transition from the sili- 
ceous material of which they were originally composed 
to calespar (fig. 14, a, 6, c); and this may be seen by 
