PLATE XVIII. 



Page 

 Fig. 1. Turonia vaiiabiUs, Mich. sp. Natural size. Showing the furrowed upper surface 



and the smooth dermal layer of the base. Probably from the Senonian of 



France 76 



F'ig. 2. Thamnospongia clavel/ata, Benett, sp. A specimen inclosed in flint. From the 



Upper Chalk at Chicklade, Wiltshire. Natural size 79 



Fig. 2 a. The same. Another flint-inclosed specimen, showing traces of longitudinal canals 



on the fractured end of one of the branches. Natural size. From the Upper 



Chalk at Stockton, Wiltshire. 

 Fig. 2 b. The same. Portion of the outer surface of a specimen from Stockton, showing 



some of the larger heads of the compound trifid spicules of the dermal layer. 



Enlarged thirty-two times. 

 Fig. 3. Thamnosponj/ia'i reticulata, Hiude. From the Grey Chalk near Folkestone. 



Natui'al size 80 



F'ig. 3 a. The same. Transverse section of one of the stems, showing the central canal and 



traces of the sinuous canals wliich open into it. Natural size. 

 F'ig. 3 b. The same. Portion of a transparent section from the interior of the sponge, 



showing the disposition of the spicular skeleton. Enlarged thirty-two times. 



The original silica of the spicules has been entirely rejjlaced by crystalline 



calcite. 

 Fig. 4. Ka/pinella patertpformis, Uinde. A vertical median section, showing the disposition 



of the canals in the sponge-wall. From the Upper Green Sand at Warminster, 



Wiltshire. Natural size 77 



Fig. 5. Pholidocladia ramosus, Hinde. Showing the empty moulds of the branches of a 



specimen in a flint from the Upper Chalk. Natui-al size 81 



Fiff 5 a. The same. A fragment of one of the branches from the interior of another flint. 



Natural size. 

 Fig. 5 b. The same. Portion of the surface of 5 a, enlarged sixty-four times, showing the 



characters of the spicular skeleton. The small square at the top of the figure 



indicates its natural size. 



