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Show 1873.] DR. J. S. B O W E R B A N K O N T H E SPONGIADcE. 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, magnified 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 interstitial membranes, magnified 80 linear. 5. A n attenuato-stellate retentive spiculum, from the interstitial membranes, magnified 530 linear. 6. One of the minute cylindro-stellate retentive spicula from the interstitial membranes, magnified 530 linear. Pachymatisma contorta, Bowerbank. Fig. 7 represents a full-sized acerate skeleton-spiculum, magnified 80 linear. 8. A n average-sized acerate skeleton-spiculum, magnified 80 linear. 9. One of the short, stout, acerate tension-spicula from the interstitial m e m branes, magnified 80 linear. 10. A fully developed attenuato-stellate retentive spiculum from the interstitial 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. A n 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-oxpando-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 interstitial 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. Tethea hispida, Bowerbank. Fig. 22 represents a fully-developed skeleton-spiculum, magnified 80 linear. This figure also represents a small-sized primary defensive spiculum. 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, magnified 250 linear. These figures 24 and 25 also represent the tension-spicula of the interstitial membranes. 26. A slender form of ovo-spinulate spiculum, occasionally intermixed with the other tension-spicula of the interstitial membranes, magnified 80 linear. |