1873.] DR. J. S. BOWERBANK ON THE SPONGIAD.E. 333 



amount of development of their radii, and also in the degree of their 

 expansion. 

 Fig. 3. One of the small acerate defensive spicula of the dermal surface, magni- 

 fied 80 linear. This figure also represents the small acerate tension- 

 spicula of the dermal membrane. 



4. One of the long, slender, and flexuous acerate tension-spicula of the in- 



terstitial membranes, magnified 80 linear. 



5. An attenuato-stellate retentive spiculum, from the interstitial mem- 



branes, magnified 530 linear. 



6. One of the minute cylindro-stellate retentive spicula from the intersti- 



tial membranes, magnified 530 linear. 



Pachymatisma contorta, Bowerbank. 

 Fig. 7 represents a full-sized acerate skeleton-spiculum, magnified SO linear. 



8. An average-sized acerate skeleton-spiculum, magnified 80 linear. 



9. One of the short, stout, acerate tension-spicula from the interstitial mem- 



branes, magnified 80 linear. 



10. A fully developed attenuato-stellate retentive spiculum from the inter- 



stitial membranes, magnified 530 linear. 



11. A very fully developed attenuato-sphero-stellate retentive spiculum 



from the interstitial membranes, magnified 530 linear. 



Geodia parasitica, Bowerbank. 



Fig. 12 represents one of the large fusiformi-acerate skeleton-spicula, magnified 

 80 linear. 



13. An average-sized attenuato-subpatento-ternate connecting-spiculum 



magnified 80 linear. 



14. One of the small and slender fusiformi-acerate tension-spicula from the 



interstitial membranes, magnified 80 linear. 



15. One of the minute sphero-stellate retentive and defensive spicula from 



the dermal membrane, magnified 530 linear. 



Geodia paupera, Bowerbank. 

 Fig. 16 represents an average-sized skeleton-spiculum, magnified 80 linear. 



17. A full-sized attenuato-expando-ternate connecting-spiculum, magnified 



80 linear. ° 



18. A small-sized attenuato-expando-ternate connecting-spiculum, magnified 



80 linear. This-sized spiculum is not uncommon intermixed with 

 the larger specimens of the same form. 



19. One of the small subfusiformi-acerate tension-spicula from the inter- 



stitial membranes, magnified 80 linear. This form also represents 

 the external defensive spicula of the porous areas. 



20. One of the largest size of cylindro-stellate retentive spicula from the 



interstitial membranes, magnified 530 linear. 



21. One of the minute cylindro-stellate retentive spicula from the interstitial 



membranes, magnified 530 linear. 



Tethca hispida, Bowerbank. 

 Fig. 22 represents a fully-developed skeleton-spiculum, magnified 80 linear 

 This figure also represents a small-sized primary defensive sni- 

 culum. r 



23. A young skeleton-spiculum, before it has developed its spinulate basal 



bulbous appendage, magnified 80 linear. 



24. One of the minute superfusiformi-ovo-spinulate spicula of the secondary 



external defensive system, magnified 80 linear. 



25. One of the same description of secondary external defensive spicula, mag- 



nified 2M linear. These figures 24 and 25 also represent the tension- 

 spicula ot the interstitial membranes. 



26. A slender form of ovo-spinulate spiculum, occasionally intermixed with 



the^ other tension -spicula of the interstitial membranes, magnified 



