68 



COELENTERATA— PORIFERA • 



PHYLUM II 



sponge are composed of vertical tubes having a radial disposition and fused 

 with one another along the sides. Between the tubes are large interstices ; 

 near the base the tubes develop hollow, spinous processes. Lattice skeleton very 

 regular, exactly similar to Coeloptijchmm. Upper Cretaceous ; Westphalia. 



Tremabolites Zitt. ; Etheridgia Tate ; Zittelispongia SinzofF, etc. Upper 

 Cretaceous. 



Camerospongia d'Orb. (Fig. 79). Globular, sub-globulai-, or pyriform. 



Fig. 79. 



Camerospongia fiingiformis 

 (Goldfuss). Planerkalk ; Oppeln, 

 Silesia. Is'atural size. 



Fig. so. 



Cystispongia lursa Quenst. Cuvieri-Planer (Turonian) ; Salz- 

 gitter, Hanover, o, Sponge, natural size ; b, Dermal layer with 

 underlying skeletal framework ; c, Skeleton, i2/j. 



Upper half of the body enveloped by smooth siliceous skin, and with large 

 circular depression on the summit ; lower half marked by undulating ridges 

 and furrows, and passing gradually into a stem. Interior of sponge body 

 consists of thin-walled, labyrinthous tubes. Upper Cretaceous. 



Cystispongia Roem. (Fig. 80). Like the preceding, but with dense siliceous 

 skin punctured by large, irregularly shaped apertures, uniformly enveloping 

 the whole sponge body. Body composed entirely of tubes. Cretaceous and 

 still living. 



Subclass 4. CALCISPONGIAE. Calcareous Sponges. 

 Skeleton composed of calcareous spicules of three-rayed, four-rayed, or uniaxial types. 



The external form of the Calcisponges is quite as variable as that of the 

 siliceous sponges, and reminds one particularly of the Lithistida. Like the 

 Lithistids, too, the thick-walled Leucones and Pharetrones have a canal-system 

 consisting of a central cavity into which radial excurrent canals conduct ; 

 while the numerous tributaries of the latter end in ciliated chambers which 

 are fed by fine incurrent canals. In the Sycones the wall is perforated by 

 simple radial tubes, but in the thin-walled Ascones it is pierced by mere holes. 



The calcareous skeletal elements lie free in the soft parts, sometimes 

 forming but a single layer disposed in the same plane {Ascones) ; sometimes 

 their disposition is more or less distinctly radial, following the canal courses 

 (Sycones) ; sometimes they are irregularly crowded together (Leucones) ; and 



