64 DK. G. J. HINDE ON CALCISPOtfGES [Feb. 19OO, 



Figs. 4-15. Three-rayed spicules from the dermal layer. Fig. 13 X 1000 ; 

 the others X200. 

 16-22, 24. Various forms of four-rayed spicules from the inner part of 



the dermal layer. X 200. 

 25, 26, 28. Minute four-rayed spicules, probably immature forms. From 

 the dermal layer. X 500. 

 Fig. 27. A four-rayed spicule, with the facial rays incipiently expanded at the 



ends. X 200. 

 Figs. 23 & 29. Immature three-rayed spicules from the dermal layer. Fig.' 23 X 

 400, and fig. 29 X 1000. 

 30-38. Three-rayed ' tuning-fork ' spicules of various forms ; the shafts 

 and the prongs are in part incomplete. From the inner portion of 

 the dermal layer. X 500. 



39 & 39a. Very slender subcylindrical spicules, pointed at both ends, either 



smooth or rough with minute prickles. From the interspaces of the 

 skeletal mesh. XoOO. 



40 & 41. Straight, styliform spicules, from the interior of the sponge. 



X500. 

 Fig. 42. Straight, pin-shaped spicule. X500. 

 Figs. 43 &44. Two imperfect cylindrical spicules, with styliform or lance-shaped 



ends ; from the outer surface of the dermal layer. x200. 

 Fig. 45. Acerate spicule from the inner portion of the dermal layer. X500. 

 Figs. 46 & 47. Elongate cylindrical spicules, from the interspaces of the mesh. 



X500. 

 48-82. Different forms of irregularly modified four-rayed spicules from 



the basal layer and from the floors or platforms traversing the sponge. 



X200. 

 Fig. 83. A small fragment of the basal layer, showing the spicules in position. 



X200. 



Plate IV. 



Plecironinia Halli (continued). 

 Fig. 1. A fragment of the outer surface of the dermal layer, showing the 

 parallel disposition of the elongated cylindrical spicules, x 200. 



2. A fragment of the basal layer. X 200. 



3. A vertical section of a portion of the basal layer. x200. 



Figs. 4& 5. Vertical sections of the skeletal mesh, showing the radial arrange- 

 ment of the apical rays of the spicules and the mode of junction of 

 the facial rays. X 60. 



Fig. 6. A broken-off fragment of the skeleton, showing the spicular structure of 

 the fibres. X60. 



7. An individual four-rayed spicule of the skeleton, showing the expanded 



terminations of the facial rays and the tapering spined apical ray. 



xioo. 



8. Another skeletal spicule, with one of the facial rays elongated and 



terminating obtusely. The spicule is invested by the tuberculated 

 calcitic pellicle which covers the mesh-fibres. X 100. 



9. A detached four-rayed spicule, in which the ends of the facial rays are 



greatly expanded, x 100. 



10. A transverse section of the skeletal mesh, showing the canals bounded 



by the spicular fibres. X 60. 



11. A vei-tical section of the liner skeletal mesh near the base of the sponge. 



X60. 



Bactronella australis, sp. nov. 

 Figs. 12-17. Specimens of various forms, showing their mode of growth. 



Natural size. From Eocene beds at Flinders (Victoria). Collected by 



Mr. T. S. Hall, M.A. 

 Fig. 18. A portion of the surface, not covered by the dermal layer, showing the 



disposition of the spicules bounding the radial canals. X 100. 

 19. Some of the apical spicular rays forming the radial fibres and the 



irregular spicules connecting them transversely, as seen in a vertical 



section. X 100. 



