»IIDER TU 



SILICISPONGIAE— LITHISTIDA 



53 



are very scarce in the Upper Jurassic (Protetraclis), but abundant in the 

 Cretaceous, Tertiary and Eecent periods. 



A'ulocopium Oswald (Fig. 48). Hemispherical or bowl-shaped with short 

 peduncle ; inferior surface covered with a dense, wrinkled, siliceous skin. 



Fig. 49. 



Callopegma acaule Zitt. Senonian ; Ahlten, Hanover ; a, Specimen in 3/^ natural size ; h, Skeleton magnified 



40/j ; c, Portion of periphery, 2/j ; d, Same magnified 40/jj and showing anchors with furcate head-rays. 



Cloaca central ; sponge body with numerous arched canals parallel to contour 

 of periphery, and with finer radial canals leading from exterior to cloaca. 

 Skeleton composed of irregulär smooth-rayed tetraclons with root-like branch- 

 ing extremities, disposed in rows parallel to the radial canals. Occurs (usually 

 replaced by calcite) in the Ordovician of the Kussian Baltic Sea Provinces, 



Fig. 50. 



Phymatella tuberosa (Quenstedt). Quadratenkreide 

 f'Upper Senonian); Linden, near Hanover. a, Sponge, 

 1/2 natural size ; b, Outer surface, 1/1 ; c, Skeletal element, 

 •'*Vl ; d, Spicules from stalk portion, 50/j. 



Fig. 51. 



Siphonia tulipa Zitt. Greensand ; Blackdown. 

 A, Longitudinalsection, natural size. B, Sponge 

 with ])eduncle and root, 1/2 natural, size (after 

 Sowerby). 



Ordovician of Illinois, and Silurian of Gotland. Also in erratic blocks on the 

 plains of Northern Germany, usually chalcedonised. 



Archaeoscyphia Hinde. Cambrian. 



Callopegma Zittel (Fig. 49). Bowl- or funnel-shaped, short-stemmed, thick- 

 walled. External surface perf orated by smaller, internal by larger canal-openings 



