Dr. G. J. Hinde on Fossil Calcispongice. 195 
the dermal spicules, a correspondence in position which con- 
clusively shows a relationship between these fossils and the 
recent examples. of the order. Beginning with the large 
* quadriradiate spicules of the dermal surface with the lateral 
rays curved away from the basal, as in figs. 1, 2, Pl. XI., we 
find closely corresponding forms in the dermal spicules of 
Leucandra Johnstonit, Carter, sp., = Leuconia nivea, Bowerb., 
Hiackel, Monogr. Bd. i. p. 216, T. 34. f. 1a. In con- 
junction with the large quadriradiates in this recent sponge, 
there are, according to Hiickel, numerous triradiates very 
variable in size and form; the majority are subregular or 
sagittal, many irregular, and few completely regular (I. 34. 
f. 1 a,6). These correspond in form, though larger in size 
than those which I have represented in figs. 9-13, 16, 17, 
Pl. XI. In this recent species Hiickel states that the three 
facial rays of the large quadriradiates lie on the dermal sur- 
face, while the apical ray bores through the wall into the 
cloacal cavity, thus corresponding in position to the dermal 
spicules of the fossil form. ame 
The pickaxe form of dermal spicule with the lateral rays 
turned towards the basal ray occurs in the surface-layer of 
Leucaltis clathria, Hickel, Monogr. Bd. 11. p. 159, T. 28. f£. 36, 
and Leucandra cucumis, Hick. Mon. p. 205, 'T. 33.f. 1f; 
but the recent forms are two or three times as large as the 
fossil. ‘The spicule represented in fig. 4, Pl. XIL., with the 
lateral rays in a straight line, also occurs in the recent Leucan- 
dra stilifera, O. Schmidt, sp., Hiick. Mon. T. 33. f. 4d. 
Coming now to the smaller spicules, the sagittal triradiates, 
represented in figs. 14, 15, are similar to the medium small tri- 
radiates of the cloacal surface of Leucaltis soda, O. Schmidt, 
sp., Hiick. Mon. T. 27. f. 3,f; but the basal ray is not so re- 
duced in these as in the fossil forms. In this recent sponge 
_ there are also small triradiates similar to those of my figures 
9-13, 24, Pl. XI. I have not been able to discover any 
spicules of recent Calcisponges which closely resemble the 
slender filiform spicules which mainly compose the fibre in 
this fossil species, figs. 18-23. The form which approaches 
the nearest is one figured by Bowerbank from Leuconia fistu- 
losa, Mon. Brit. Sp. vol. ii. pl. v. f. 16; but in this the 
basal ray, though small, is by no means reduced to the insig- 
nificant proportions of that of the fossil. 
Whilst tle various forms of spicules present in this fossil 
thus closely resemble the spicules in recent Calcisponges, they 
do not correspond to the spicules of any known siliceous 
sponge, whether fossil or recent. ‘The skeleton of some sili- 
ceous tetractinellid sponges is built up of three- and four-rayed 
