40 



DAWSON AND HINDB 



2. — Protospongia mononema, S.N. 



(Figs. 5, 6 and 1. PI. Ill, fig. 3.) 



General size abont on»' inch in diameter, originally globular but now flattened. 

 Body spicTiles cruciform and more slender than those of P. tetranema. Superficial or 

 defensive spicules very numerous and somewhat long and slender, so as to give a hirsute 



Fig. 5. — Protospongia mononema. 

 Restored. 



Fig. 6. — Protusponyia mononema. Cruciform and pro- 

 tective spicules, X 5. 



Eoot, single, 



api^earance and in flattened specimens often to obscure the body spicules 

 stout, often three inches long, with two to four short spreading branches at base. These 

 terminal spicules are flattened at the extremities. Hinde remarks that some specimens 

 seem to have two or more anchoring rods ; but in all or most of the specimens showing 



Fig. 7. — Protospongia mononema. Primary, secondary 

 and tertiary spinules, x5. 



this appearance these seem to have been loose rods drifted into contact with the sponge. 

 The anchoring rod in this species is often increased in thickness]^by a crust or frosting of 

 pyrite, and this would seem to indicate that it had, like the modern Hyalonema, animal 

 matter as well as silica in its composition. 



