202 DR. J. S. BOWERBANK ON SPONGIAD^. [Feb. 20, 



Fig. 6. One of the small fusiformi-acerate tension-spicula from the dermal 

 membrane of one of the porous areas, magnified 80 linear. 



Fig. 7. A large attenuato-patento-ternate connecting spiculum, magnified 80 

 linear. 



Fig. 8. A furcated attenuato-patento-ternate connecting spiculum, magnified 

 80 linear. 



Fig. 9. One of the recurvo-ternate spicula from immediately beneath the ex- 

 ternal crust of the sponge, magnified 80 linear. 



Fig. 10. About half of one of the large fusiformi-acerate skeleton-spicula, mag- 

 nified 80 linear. 



Fig. 11. An ovary from the external surface of the sponge, magnified 108 linear. 



Fig. 12. The foramen of one of the ovaries, showing the funnel-shaped disposi- 

 tion of the spicula, magnified 308 linear. 



For further illustration of the structure of the ovaries of this sponge I must 

 refer the reader to the ' Philosophical Transactions of the Royal Society ' for 

 1862, pi. xxxiv. figs. 2, 3, 4, 5, 6 : — Fig. 2 representing an ovarium in very nearly 

 an adult state, magnified 183 linear. Fig. 3. A small portion of the surface of 

 an adult ovarium, exhibiting the foramen, magnified 308 linear. Fig. 4. A por- 

 tion of a young ovarium with the distal points of its spicula acutely terminated, 

 not being fully developed, magnified 308 linear. Fig. 5. A section through 

 nearly the centre of a mature ovarium, showing the radiation of its spicula 

 from near the centre to its circumference, magnified 308 linear. Fig 6. Two 

 ovaria, (a) containing about the maximum of ova, (b) after a great part of the 

 ova have been discharged, magnified 108 linear. 



Figures similar to those referred to in the ' Philosophical Transactions ' may 

 also be seen in ' Monograph of British Spongiadse,' vol. i. figs. 325-329. 



Plate XI. 



Geodia Barrctti, Bowerbank. 



Fig. 1. Represents the type specimen of the species, natural size. 



Fig. 2. One of the large fusiformi-acerate spicula, representing both the large 

 external defensive and the skeleton-spicula, magnified 80 linear. 



Fig. 3. One of the small fusiformi-acerate spicula which form the secondary 

 system of external defensive spicula, magnified 80 linear. These spi- 

 cula are identical with the tension-spicula of the interstitial membranes, 

 the same figure serving to represent both. 



Fig. 4. The head of one of the large attenuato-furcated patento-ternate connect- 

 ing spicula, abundant immediately beneath the dermal crust of the 

 sponge, magnified 80 linear. The shafts of these spicula are rather 

 stouter and nearly twice the length of the skeleton ones ; they are fre- 

 quently one sixth or one fifth of an inch in length. 



Fig. 5. An attenuato-recurvo-ternate spiculum of the normal form, magnified 

 80 linear. The heads of these spicula are subject to frequent dis- 

 tortions. 



Fig. 6. Represents one of the most singular of the numerous distortions of the 

 heads of the recurvo-ternate spicula, the radii in which are double the 

 usual number, magnified 80 linear. By an oversight of the artist, a 

 figure of the minute cylindro-stellate retentive spicula of the dermal 

 and interstitial membranes has been omitted ; but a reference to those 

 of G. M'Andrewii will afford an accurate idea of their form. 



Fig. 7. One of the ovaria, magnified 250 linear. 



For further information regarding the anatomy of this sponge I must refer 

 the reader to the ' Philosophical Transactions of the Royal Society' for 1862 — 

 pi. xxxii. fig. 2, for a section of the sponge at right angles to its surface ; fig. 3 

 for a view of a small portion of the dermal crust ; and fig. 4 for a group of the 

 inhalant pores. Similar figures will also be found in ' Monograph of British 

 Spongiadse,' figs. 354, 301, and 302. 



