PLATE XXin. 



Page 

 rig. 1. Astylospongia? Rameri, Hinde. An imperfect silieified specimen, showing the 



disposition of the surface-canals and the apertures of the radial canals. Natural 



size. Probably from Silurian strata 92 



Fig. 1 a. The same. A transverse section of fig. 1, showing the course of the radial canals. 



Natural size. 

 Fig. 1 b. The same. Showing the spicular structure of the interior, enlarged sixty-four 



times. Drawn from a transparent section by means of the camera lucida. 

 Fig. 2. Craticularia Fittoni, Mantell, sp. An imperfect specimen from the Grey Chalk 



near Dover. Natural size 94 



Fig. 2 a. The same. Portion of the outer surface of a specimen from the Chalk Marl near 



Ventnor, Isle of Wight, showing the character of the dermal layer. Enlarged 



sixty-four times. 

 Fig. 2 b. The same. A fragment of the spicular mesh of the interior of the wall. Enlarged 



sixty-four times. 

 Jig. 3. Strephinia convoluta, Hinde. An imperfect specimen from the Grey Chalk near 



Dover. Natural size 96 



Fig. 3 a. The same. A transverse section of a portion of the wall, showing its thickness 



and the disposition of the canals. Natural size. The shaded portion of the 



figure represents the spicular wall, and the lighter parts the canals. In places 



the canals appear to extend quite through the wall, but this is owing to the 



thinness of the wall at the extremity of the blind canals, so that it readily breaks 



away when the surface is polished. 

 Fig. 3 b. The same. Portion oi: fig. 3 a, enlarged sixty-four times, showing the spicular 



structure of the wall. The spicules have been entirely replaced by calcite of a 



tint slightly darker than the chalky matrix. 

 Fig. 4. Strephinia reteformis , Hinde. Natural size. Showing the reticulate character of 



the outer surface. From the Grey Chalk near Dover 97 



Fig. 4 a. The same. A vertical median section of fig. 4, showing the thickness of the wall 



and the disposition of the canals. The spicular structure of this specimen, like 



that of S. convoluta, has been replaced by calcite, and the walls at the extremity 



of the canals have been partially broken away. 



