PLATE XV. 



Page 

 Fig. 1. HaUirhoa agariciformis , Benett, sp. Showing the upper surface and the open 



canals extending downwards from the cloaca. Natural size. From the Upper 



Green Sand at Warminster, Wiltshire 69 



Fig. 1 a. The same. Two spicules from the interior mesh of another Warminster specimen. 



Enlarged seventy-two times. Drawn from a transparent section by means of 



the camera lucida. 

 Fig. 1 b. The same. Portion of the outer surface of a specimen in which the dermal layer 



has been preserved, showing the laciniatcd disciform heads of its component 



spicules. Enlarged thirty-two times. The specimen is from Warminster, and 



belongs to the Jermyn- Street Museum. 

 Fig. 2. Jerea reticulata, Hinde. A specimen from the Gres Vert at Rettsel, Ardennes, 



showing the reticulate disposition of the canals on the outer surface. Natural 



size. The canals in this specimen have been infilled with siliceous material, 



and now appear as solid fibres 70 



Fig. 2 a. The same. The summit of the same specimen, showing the close arrangement of 



the canal-apertures. Natural size. 

 Fig. 2 6. The same. A vertical median section of a specimen from the Upper Green Sand 



at Warminster, showing the disposition of the radial canals. Natural size. 

 Fig. 3. Jerea cordiformis, Hinde. From the Grey Chalk near Dover. Natural size . . 71 

 Fig. 3 a. The same. A vertical median section of the same specimen, showing the direction 



of the vertical and radial canals. Natural size. 



