34 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallery X. Hyaloiieniatidai or Glass-rope Sponges, some of which are 
Table-case found fossil as for back as the Silurian. There are a number 
Wali-case families : Protospongidm (Cambrian and Silurian) ; 
8b, 8c. Dictyospongidm (Silurian and Devonian) ; Plectospongidm 
(Ordovician and Silurian) ; Brachiospongidae (Silurian) ; 
Table-case I’ollakidse (Carbonifei’ous and Cretaceous), and others. Here 
also have been placed the peculiar Receptaculitidae (Ordo- 
Table-case vician to Carboniferous), but it has been shown that their 
spicules were probably calcareous, and, although still 
.OSP 
Fig. 10. — Reconstruction of Ventriculites, a Dictyonine Hexactinellid 
sponge from the English Chalk, r, root-like processes of attachment ; 
osc, osculum leading from the cloaca. A piece of the margin is broken 
away to show the folds, which form the incurrent and excurrent canals. 
(After E. A. Minchin in E. Ray Lankester’s “ Treatise on Zoology.” 
By permission of the Editor.) 
exhibited near the sponges for the sake of convenience, they 
are now not considered to be sponges at all. Some suppose 
them to be calcareous algoe. 
SuB-ChASS II. — DICTYONINA. The six-rayed spicules 
of the middle layers of the body-wall overlap by their ends 
and are then fused by a deposit of silica into a network, or 
rather rafterwork, with square meshes (Greek dictyon, a net). 
Owing to their strong skeleton many Dictyonina are well 
preserved as fossils, representing the following families : — 
