PLATE XXVIII. 



Page 



Fig. 1. Cincliderma quadratum, Hinde. The upper portion of a funnel-shaped specimen, 

 from the Upper Chalk of the South of England, showing the dermal layer. 

 Natural size 128 



Fig. 1 a. The same. The basal portion of a specimen. Natural size. 



Fig. 1 b. The same. A median vertical section of 1 a, natural size, showing the disposition 

 of the anastomosing wall-plaits in the interior of the sponge. 



Fig. 1 c. The same. Portion of the spicular structure of the interior wall-plaits, enlarged 

 thirty times. The spicules have been dissolved and only empty moulds remain. 



Fig. 1 d. The same. Portion of the dermal layer of 1 a, enlarged fifteen times. The spiciiles 

 are only indicated by hollow moulds in the chalky matrix. The minute spicules 

 forming the layer between the framework of larger spicules are too small and 

 too thickly intermingled together to be clearly delineated. 



Fig. 2. Proiosponffiafenestrata, Salter. A fi-agment of a specimen preserved in indurated 

 black shale. Enlarged five times. Prom Menevian strata at St. David's, South 

 Wales. The spicular framework is now composed of iron pyrites ; it has evi- 

 dently been distorted by pressure from its original rectangular form. The 

 figure is drawn from Salter's type specimen 129 



Fig. 3. Dictyophyton tuberosum, Conrad, sp. An imperfect specimen preserved in sand- 

 stone, natural size. From the Chemung gi'oup of the Upper Devonian at 

 Cohocton, Steuben County, "Western New York 130 



Fig. 4. Plocoscyphia fenestrata, T. Smith, sp. A specimen from the Upper Green Sand 

 at Folkestone, showing the disposition of the tubes at the surface. Natural 

 size 133 



Fig. 4 a. The same. A transverse section of a smaller specimen from the same locality, 

 showing the arrangement of the wall-plaits of the interior of the sponge. 

 Natural size. 



Fig. 4 b. The same. A fragment of the spicular mesh of the interior of the wall -plaits, 

 enlarged thirty times. 



Fig. 4 c. The same. A portion of the dermal layer of the wall, enlarged thirty times. 



