Plate 17. 



Fig. 1. Pachi/challna acapulccnsis. 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, /. b., is cut transversely. Skeletal 

 network comparatively regular; s. v., surface 

 villi; x20. 



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



4. " " Small connective ; x 300. 



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



X 300. 



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



7. Petrosia slmilis densissima. Prom a photograph ; {. 



8. Occanapia baciJlifera. Surface of fistula ; x 100. 



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



10. Petrosia sirnilis densissima. Oxea and flagellated chambers, one of which ojsens 



into efferent canal ; x 250. 



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



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



13. Pacliychalina acapulcensis. Longitudinal section through macerated conulus. 



An axial bundle of spiculo-fibre gives off, and 

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

 villi; X 20. 



