432 On CarhomferonH Sponges from Ayr slave. 



furnace, on account of the quantity of silica which cements the 

 organisms. The masses of flint seem in places to have 

 squeezed the matrix around them as if by expansion. The 

 calcareous organisms enclosed are entirely silicified, the cal- 

 cite being wholly replaced. 



EXPLANATION OF PLATES XIV. & XV. 



[All the figures were drawn by camera lucida. Fig. 4 is natural size ; 

 the actual sizes of the othei^s are indicated alongside of the tigures. 



I omitted to tell the lithographers that the plates had been drawn seven 

 months ago, and had not been retouched. .Where the finer lines were 

 found to have disappeared the lithogTaphers took every pains to compen- 

 sate for my neglect.] 



A., specimens in Mr. Armstrong's Cabinet; S., in Mr. Smith's ; 

 Y., m Mr. Young's. 



Fig. 1. Hyalonema Smithii, n. sp. Fragment of rope. Cunningham 

 Baidlaud. Y^ 



Fig. 2. End view of same specimen. 



Fig. 3. H. Smithii. A few of the rods, enlarged, to show varymg diame- 

 ters in bundle. 



Fig. 4. The same, showing sexradiate spicules alongside of rope. Auchen- 

 skepch. Y. 



Figs. 5 and 6. The same, showing removal of rod and replacement of 

 central canal by siHceous rod. Y. 



Figs. 7 and 8. The same, transverse section of rods. Y. 



Fig. 9. The same, vertical section of rod, showing central canal and striae 

 answering to concentric layers. Y . 



Fig. 10. The same, botryoidal structure. Y. 



Figs. 11, 12, 12 a, 14, 20, 21, 22, 23. The same, sexradiate spicules of 

 various types. Y. 



Figs. 13, 19, 26. The same, stellate spicules, smooth. Y. 



Figs. 15, 16, 17, 25. The same, anchoring booklets. Y''. 



Fig. 24. Stellate spicule, cusliioned. Y. 



Figs. 27, 29. Stellate spicules, pustulate. Y. 



Figs- 18, 28, 42, 43. Chlamys magna. Biteniate spicules. Y. and S. 



Fig. 30. Hyalonema Smithii. Nail-like spicules matted together in posi- 

 tion. 



Fig. 31. Maplistimi Armstrongi, n. sp. A. 



Figs. 32, 33. The same. Successive enlargement of part of surface of 

 fig. 31. In fig. 33 the simple fibres are well seen, and their 

 truncated ends on the knobs. 



Figs. 34, 35. The same. Opposite faces of another specimen, sliowing 

 oscula and internal canals. A. 



Fig. 36. The same. Enlargement of part of fig. 34. 



Fig. 37. The same, showing unusually prominent ridges. A. 



Figs. 38, 39, 40. Undetermined forms. S. 



Fig. 41. Incrusting sponge?, hollow, tubular. Y. 



Figs. 44-51. Various branching forms from the rotten limestone. S. 



