63) DR. J. S. BOWERBANK ON THE SPONGIAD.E. [May 7, 



DESCRIPTION OF THE PLATES. 

 Plate XLVI. 



Fig. 1. The type specimen of Geodia tuberculosa, PJowerbank, natural size. 

 Fig. 2. One of the large fusiformi-acerate skeleton-spicula, magnified 80 linear. 



This figure also represents a large primary external defensive spiculum. 

 Fig. 3. A secondary external defensive spiculum, magnified 80 linear. 

 Fig. 4. One of the patento-ternate connecting spicula of the normal form, mag- 

 nified 80 linear. 

 Fig. 5. A large and very fully developed patento-ternate connecting spiculum 



with the distal terminations of the radii recurved, magnified 80 linear. 

 Fig. G. A recurvo-ternate spiculum from immediately beneath the dermal crust, 



magnified 80 linear. 

 Fig. 7. A porrecto-ternate spiculum from a short distance beneath the dermal 



crust, magnified 80 li.iear. 

 Fig. 8. One of the minute subsphero-cylindro-stellate spicula from the dermal 



membrane, magnified 530 linear. 

 Fig. 9. One of the slender acerate tension-spicula of the interstitial membranes, 



magnified 80 linear. 

 Fig. 10. One of the comparatively large attenuato-stellate retentive spicula of 



the interstitial membranes, magnified 530 linear. 

 Fig. 11. A large cylindro-stellate spiculum with radii spinous, magnified 530 



linear. These spicula are very few in number. 



Plate XLVII. 



Fig. 1. The type specimen of Geodia ttmulosa from Honduras, natural size. 



Fig. 2. One of the slender acerate tension-spicula from the porous areas, mag- 

 nified 80 linear. 



Fig. 3. A minute eylindro-subsphero-stellate sjjiculum from a porous area, 

 magnified 530 linear. These spicula vary to a considerable degree in 

 size and completeness of development ; the one figured is a mature 

 one. 



Fig. 4. A fully developed attenuato-patento-ternate connecting spiculum, mag- 

 nified 80 linear. 



Fig. 5. An attenuato-patento-ternate connecting spiculum in an early stage of 

 development, magnified 80 linear. 



Fig. 6. A fusiformi-acerate skeleton-spiculum, magnified 80 linear. 



Fig. 7. One of the tension-spicula from the interstitial membranes, magnified 

 80 linear. 



Fig. 8. One of the comparatively large attenuato-stellate retentive spicula of the 

 interstitial membranes, magnified 530 linear. 



Plate XLVIII. 



Fig. 1. The type specimen of Pachymatisma areolata, Bowerbank, natural 

 size. 



Fig. 2. One of the large external defensive spicula, magnified 80 linear. This 

 form also occurs to a great extent in the skeleton. 



Fig. 3. An external defensive spiculum of the secondary series from the dermal 

 surface, magnified 80 linear. These spicula vary to some extent in 

 size and form. 



Fig. 4. A skeleton fusiformi-acerate spiculum with very blunt terminations, 

 magnified 80 linear. These spicula vary in their terminations in every 

 degree between figs. 2 and 4. 



Fig. 5. One of the large attenuato-stellate retentive spicula of the dermal mem- 

 brane, magnified 530 linear. 



Fig. 6. A fusiformi-cylindrical, incipiently spined minute sphero-stellate reten- 

 tive spicidum from the dermal membrane, magnified 530 linear. 



