It) SPONGARIUM INTERRUPTUM (JPCoy). Natural size, from the Upper Ludlow Rock of Kendal, 

 shewing the attachment of the base and peculiar interrupted markings. 



1 (j a Portion of surface magnified two diameters. 



17 Portion of specimen, shewing the upper concave concentrically wrinkled surface, and at the upper corner 



a portion broken away, leaving the impression of the radiated exterior on the supporting matrix. 



18 CLISISOPHYLLUM VORTEX (^PCoy). Natural size, from Wenlock. 



18 a Vertical and horizontal sections near base. Natural size, shewing the very large vesicular inner area of rows 



of upward-curved cells, the narrow outer area containing the primary radiating lamellae in the horizontal 

 section and large vesicular tissue in the vertical section ; and the extremely narrow layer of minute vesicular 

 tissue lining the wall and corresponding to the short secondary lamella; on the horizontal section. 



19 CYSTIPHYLLUM BREVILAMELLATUM (M^Coy). Natural size, from Wenlock. 



19 a Vertical and horizontal sections, the former shewing the loose vesicular tissue in rows gradually curving 



downwards, the cells being much larger in the middle than at the sides, where they correspond to the small 

 lamelliferous area of the horizontal section. 



20 STREPHODES PSEUDO-CERATITES, (M^Coy). Natural'size, from the Limestone of Old Radnor, Presteigne. 



20 a Vertical and horizontal sections, shewing the filling up of the base, and thick lining of the outer area with 



nearly solid sclerenchyme. 



21 STREPHODES TROCHIFORMIS (M=Coy). Natural size, from Dudley. 



22 STREPHODES VERMICULOIDES (M=Coy). Portion of large group natural size, from near Aymestry, shewing 



the form of the deep cups lined with strong lamellje, and the latter becoming obscure on the thick obtuse margin. 



22 a Portion, natural size, vertical and horizontal sections, the former shewing the very loose vesicular tissue of 



the central area and wide lining of the walls, with nearly solid sclerenchyme ; the latter shewing the primary 

 radiating lamelhe extending to the centre, and the secondary ones barely projecting within the wide sclerenchyme 

 lining, through which the lamellee may be obscurely discerned. 



23 PETRAIA ^IIQUISULCATA (M<^Coy). Average-sized specimen, from Coniston, shewing the equal lamellar 



sulci and portion of the epitheca towards the base. 



24 Shewing the form of terminal cup, with the lamella uniting in pairs without vesicular connecting plates ; and 



vertical fracture, shewing the conical twisting of the lamellae in the centre. 



25 PETRAIA UNISERIALIS (M=Coy). Natural size of cast, from the slates of Llansantfraid. 



25 a Two of the interlamellar projections of the cast, magnified three diameters, each with a small row of puncta 



corresponding to the secondary lamella?, and divided by the deep slit corresponding to one of the primary lamellse. 



26 PETRAIA SUBDUPLICATA (M'Coy). Natural size, from the Caradoc Sandstone of Dalquorhan, shewing the 



cast of the cup above, and a rough vertical section of the dense deposit of sclerenchyme which fills the base 

 and lines the wall. 



26 o Two of the interlamellar projections magnified two diameters, shewing the slits of the primary and secondary 



lamella\ 



26 b Two of the interlamellar projections of the var. crenulata. 



27 ARACHNOPHYLLUM TYPUS (M°Coy). Natural size, from Aymestry, portion of large mass. 



27 a Portion of ditto magnified three diameters, shewing the form of the cup, with the strong lamell* lining the 



depressed centre, becoming abruptly thinner, more numerous by branching, and flexuous, as they pass irregularly 

 into those of the adjoining stars ; the vertical section in lower part shewing the uniform vesicular tissue of the 

 whole mass without divisional walls to the cells : the few vertical lines under the centre are divided edges of 

 some of the lamells. 



28 STROMBODES WENLOCKENSIS (M'=Coy). Portion of large mass natural size, from Wenlock. 



28 a Vertical section shewing the strong divisional walls bounding the axis, the inner area, and the individual stars, 



as well as the peculiar tissues of each. 



