PLATE IV. 



IsoDiOTTA sciTULA, Bowerbauk. 



Figs, la, lb, Ic. — ^Aouate spicules of the skeleton, 

 to show their variation in size. X 150. 



Fig. 2. — One of the bidentate, equi-anchorate, reten- 

 tive spieula. X 800. 



Figs. 3a and 3b. — Angulated bihamate spioula of the 

 dermal membrane, more abundant than the last but 

 not mentioned in the description of the species. 

 X 800. 



For figures of the sponge itself see Plate IX, figs. 

 1—3. 



HYMENiACiDoiir viEGULATUS, BowerbanJc. 



Fig. 4. — The sponge. Natural size. 

 Fig. 5. — One of the long, slender, aouate spieula of 

 the skeleton. X 150. 



HiMENiAoiDON CALLOsus, Bowerbank. 



Figs. 6 and 7. — The type-specimens of the sponge. 

 Natural size. 



Fig. 8. — One of the acuate spieula of the skeleton, 

 X 150. 



[Fig. 9. — A hydroid zoophyte, parasitical on H. cal- 

 losus, and inserted in the Plate by the engraver by 

 mistake.] 



Htmeniaoidon aemiger, Bowerbank. 



Fig. 10. — Hymeniacidon armiger. Natural size. 

 Thinly coating the basal portion of a specimen of 

 NulUpora polymorpha. 



Figs. 11, 12 and 13. — Attenuato-aouate, entirely 

 spined, dermal spicules, showing their variability in 

 size. X 150. 



Fig. 14. — A fusiformi-acerate spicule of the skele- 

 ton. X 150. 



Fig. 15. — A bidentate equi-anchorate spicule of the 

 dermal membrane. X 800. 



Figs. 16 and 17. Tridentate, equi-anchorate, reten- 

 tive spieula. X 800. 



