432 On Carhoniferoufi Sponges from Ayrshire. 



furnace, ou account of the quantitj 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 tlie figures were drawn by camera lucida. Fig. 4 is natiu'al size ; 

 the actual sizes of the others are indicated alongside of the figures. 



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 lithographers took eveiy pains to compen- 

 sate for my neglect.] 



A., specimens in ^Ir. Armsti-ong's Cabinet; S., in Mr. Smith's ; 

 Y., in Mr. Young's. 



Fig. 1. Kyalonema S'mithii, n. sp. Fragment of rope. Cunningham 

 Baidland. Y. 



Fig. 2. End -^iew of same specimen. 



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

 ters in bundle. 



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

 skeoch. Y. 



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

 central canal by siUceous rod. IT. 



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



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

 answering to concentric layers. Y. 



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



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

 various types. Y. 



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



Figs. 15, 10, 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. Bitemate spicules. Y. and S. 



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

 tion. 



Fig. 31. HapKsticyn Armstroyigi, n. sp. A. 



Figs. 32, 33. The same. Successive enlargement of part of sui-face of 

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

 truncated ends on the knobs. 



Figs. 34, 3o. The same. Opposite faces of another specimen, showing 

 oscida 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. Vaiious branching forms from the rotten limestone. S. 



