176 



PORIFERA. 



As regards the remaining groups of the Cretaceous Hexactinellids, 

 the body-wall in the family Callodictyonidce is composed of hexacti- 

 nellid spicules the nodes of which are octahedral, and which give 

 rise by their union to an exceedingly regular open meshwork, while 

 the canal-system is wanting or rudimentary. The Cretaceous genera 





Fig. 66. — Canierospongiafungiformis. Cretaceous. 



Callodictyon and Plenrope are good representatives of this family. 

 In the Mellitionidce, are included Sponges in which the walls are 

 closely perforated by tubular canals like the cells of honeycomb, and 

 the spicules have simple nodes. This family includes the Creta- 

 ceous genus Stauronema and the genus Aphrocallistes, which ranges 

 from the Chalk to the present day. The family of the Coscinopori- 



dce comprises variously shaped 

 Sponges, with a close and irre- 

 gular skeletal network, and hav- 

 ing numerous straight, blind, 

 radiate canals which open alter- 

 nately on both sides of the 

 sponge - wall. In Cosrinopora 

 itself (fig. 67), the cup-shaped 

 sponge-body is affixed to some 

 foreign object by ramified roots. 

 The lattice-work of the skeleton 

 is irregular, and the crossing- 

 nodes of the spicules are partly 

 solid and partly furnished with 

 a " lantern." In the nearly 

 allied Guettardia, which is also 

 Cretaceous in its range, the wall is deeply folded in a stellate 

 manner, and the crossing-nodes of the spicules are solid. Nearly 

 related to the preceding is the family of the Stanrodermidce, which, 

 though principally Jurassic in its range, is not without Cretaceous 

 representatives (such as Eubrochus). 



The Tertiary Hexactinellids, finally, are comparatively few in num- 

 ber and are imperfectly known, but the order is represented at the 

 present day by such genera as Euplectella, Hyalonema, Aphrocallistes, 

 Holtenia, Enrete, Earrea, and many others. 



Before leaving the Hexactinellid Sponges, a few words may be 

 added with regard to the Silurian genus Amphispongia, the char- 



Fig. 67. — Coscinopora czipuliformis, and a por- 

 tion of its surface enlarged. Cretaceous. 



