38 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallei-yX. are closely apposed to the axis and branches of adjoining 
spicules so as to form loosely arranged fdn-es or an irregular 
meslnvork (Fig. 12 a, h ) the Cretaceous Verruculina 
(Fig. 17) is characteristic. 
Sub-Class II. — monactinellida. Deinospongiae 
with monaxon spicules. 
The chief modifications of this simple type of spicule 
are shown in the accompanying figure (Fig. 14-a-g'). With 
Fig. 14. — Fossil sponge spicules : Silicispongiae, Monactinellida. a-q are 
skeletal, r, s, t are flosli-spicules. An open axial canal is shown in /; 
a closed canal in g. a, c, enlarged 26 diam. ; b, 100 diam. ; c, /, g, i, j, 
k, q, 40 diam. ; d, 66 diam. ; h, m, n, o, r, s, t, li4 diam. ; I, p, 13 diam. 
(After Hinde.) 
these are associated smaller flesh-spicules, serving as grapnels 
in those forms that have a harder outer skin or cortex 
(Fig. 14 r, s, t). In these latter, constituting the Order 
Hadromerina or Spintharophora, the spicules are loosely 
and irregularly arranged. In the other Order, Halichon- 
drina, the siliceous spicules are bound into a skeleton by 
the horny sub.stance spongin. Consequently, though the 
spicules abound in siliceous deposits, chiefly of Tertiary age. 
Table-cases complete sponges are rarely preserved. Chalina, Rcnicra, 
16 , 14 . and the freshwater Spongillct are among fossil representatives 
Table-case of the Halichondrina. The Hadromerina are important to 
tt- geologists from including the boring CTionidae, whose tubes 
are often seen traversing fossil shells ; indeed they are also 
active in the disintegration of rocks. 
Class IV. (?) OCTACTINELLIDA. 
Silicisjiongiae, in which the normal spicule has eight 
rays, of which six radiate in one plane from a common 
centre, while the other two radiate from the same centre at 
