172 Mr. H. J. Carter on the Identity 
the Spongida,” viz. that “ where a spicule which has a point 
projects beyond the surface of the sponge to which it belongs, 
that point will be always outermost” (‘ Annals,’ 1875, vol. 
xvi. p. 16); for this is by no means the case, since where 
the spicule is intended for anchoring, or for binding down 
the surface-spicules of the body of the sponge, and by thus 
intermingling with each other to form a kind of crust, the 
branched head is outwards and the pointed end of the shaft 
inwards. 
Thus in the anchoring spicules of the hexactinellids Rossella 
and Huplectella, in Geodra, in Stelletta (especially Wyville- 
thomsonia Wallicht’), and in Tethya (type T. cranium), also 
in some of the calcareous sponges, the former is the case ; 
while the large surface-spicules on the body of Rossella and 
many other hexactinellids, together with the large trifid 
( zone-”) spicules of Geodia and Stelletta, especially in 
Wyvillethomsonia Wallichit, all the Lithistids, and some of 
the calcareous sponges (ex. gr. Leuconia Johnstonit, ‘ Annals,’ 
1871, vol. viii. pl. 1. fig. 6) furnish instances of the latter. 
Yet in other cases, where the spicules are not branched, but 
linear and pointed at both ends, especially in the Renierida, 
the points bristle on the surface ; and that this would be the 
case if one end were obtuse, is evidenced by the Suberitida, in 
which the pin-like spicule always holds this position. ven 
in Placospongia melobesioides and Xenospongia patelliformis, 
in which the crusts respectively are composed of a layer of 
Geodia-like siliceous balls and Stelletta-like stellates, accom- 
panied by a pin-like skeleton-spicule only, the point of the 
latter is outwards. ? 
Therefore in the “ Notes &c.” to which I have above alluded, 
it should have been stated, in the section immediately following 
the tabular view of the skeleton-spicules therein given, that 
while the spicules of the “ linear group” have their pointed 
ends directed outwards, the reverse is the case with the 
“‘ramular group.” How this omission occurred I cannot 
conceive, as the last spicules mentioned in this table are the 
“ anchoring ” ones of the Hexactinellida. Thus it is rather 
an error of omission than of commission, of which, I fear, 
many more will be found in my “ Notes.” 
PostTscRIPT. 
On the Identity of Squamulina scopula with the Sponges. 
In a paper entitled ‘‘ Observations upon Professor Ernst 
Hickel’s Group ‘ Physemaria,’ and on the Affinity of the 
Sponges,’ Mr. Saville Kent, in the last number of the 
