SPONGIDA. 



147 



discovered, but the family survives in the existing genus 

 Myliusia. Of the remaining Cretaceous Hexactinellits, we 

 may just mention Coscinopora (fig. 43), with its cup-sharad 

 skeleton affixed to foreign bodies by ramified roots, 



Fig. 42. Camerospongia fung iformis. Cretaceous. 



lattice-work of the skeleton is irregular, and the 



nodes of the spicules are partly solid, and partly furnished 



with a " lantern." In the nearly allied Guettardia the wall 



is deeply folded in a stellate 



manner, and the crossing- 



nodes are solid. Lastly, we 



find in the Cretaceous the 



first representative of the cu- 



rious modern genus Aphro- 



callistcs. 



In the Tertiary period 

 comparatively few Hexac- 

 tinellids make their appear- 

 ance, doubtless owing to the 

 fact that so many of the 



of this ao-P arp 



Fig ' 4:i> - Coscin P ra wpuUJurm is, and a por- 



shallow -water deposits. In 

 the Miocene of Oran, in North 



tion of its surface enlarged. Cretaceous. 



Africa, however, an abun- 



dance of Hexactinellids (Craticularia, Aphrocallistes, &c.) 

 have been detected. 



At the present day, we find an abundance of Hexacti- 

 nellid Sponges, of which the most striking forms are the ex- 

 clusively recent Euplectellidce, in which the skeleton-spicules 

 are cemented together into a ladder-like trellis-work, and 

 there is a single " osculum " provided with a porous lid. 



(B.) Section Lithistidcc. In this group are comprised 

 Siliceous Sponges in which the spicules are fundamentally 

 quadriradiate, three of the four arms being so disposed as to 



