Plate 17. 



Fig. 1. PacliychaUna acapulcensis. Dermal membrane. Pores and dermal reticulum 



with villi. Surface preparation ; x 70. 

 " 2. " " Horizontal section, vertical to surface, of macerated 



sponge. Surface of sponge above. A longitudinal 

 skeletal bundle, /. h., is cut transversely. Skeletal 

 network comparatively regular; s. v., surface 

 villi; X 20. 



3. " " Large radial skeletal fibre ; x 300. 



4. " " Small connective ; x 300. 



5. " " One of the finest fibres, subdividing a skeletal mesh ; 



x300. 



6. Petrosia varluhills crassa. Oxeas, with spongin ; x 100. 



7. Petrosia similis densissima. From a photograph ; \. 



8. Oceanapia hacillifera. Surface of fistula ; x 100. 



9. Petrosia variabilis crassa. From a photograph ; ]■. 



10. Petrosia similis densissima. Oxea and flagellated chambers, one of which opens 



into efferent canal ; x 250. 



11. Gellius perforatus. End of skeletal oxea, with sigmata; x 450. 



12. Petrosia variabilis crassa. From a photograph ; \. 



13. PacliychaUna acapulcensis. Longitudinal section through macerated conulus. 



An axial bundle of spiculo-fibre gives off, and 

 ultimately divides into, radial fibres; s. o., surface 

 villi; X 20. 



