304 DR. J. S. BOWERBANK ON THE SPONGIADjE. [May 5, 



Hab. South Seas. 

 Examined in the dried state. 



The specimen figured is the only one that I have seen. I ob- 

 tained it by purchase from a dealer, along with other sponges and 

 specimens of Oculina rosea from the South Seas. The external cha- 

 racters of this sponge at once separate it from the nearly allied 

 species H. ventriculoides. The outer surface exhibits but very 

 faint traces of the primary radial lines of the skeleton that are so 

 prominently exhibited in H. ventriculoides ; and on the inner surface 

 the radial lines are so much depressed as to be scarcely termed 

 elevated. The retiform dermis is abundantly supplied with arena- 

 ceous particles of nearly uniform size. The oscula are nearly all 

 obsolete ; the few seen by the aid of a lens of two inches focus were 

 minute simple orifices. The pores are readily to be seen by the aid 

 of the lens ; they are very numerous on the outer or inhalant surface 

 of the sponge, and are equally dispersed on all parts of its surface. 

 The primary lines of the skeleton are abundantly arenulous, the 

 grains of sand usually forming a single series very equable in size. 



The secondary skeleton-fibres rarely ever contain sand particles ; 

 but a few small fragments of siliceous spicula are occasionally seen 

 in some of them, and they always appear to be disposed in accordance 

 with the axis of the fibre. This species appears to be closely allied 

 to Mantell's Spongus Townsendi, p. 164, tab. xvi. fig. 9, 'Geology 

 of Sussex.' The only portion of the ventriculite sponge in Man- 

 tell's figure that is visible is the extremely thin distal margin of the 

 sponge ; and in this character it closely resembles our recent speci- 

 men. I have not been fortunate enough to meet with a good spe- 

 cimen of Mantell's S. Townsendi; but I have a portion of what is 

 apparently one of them completely immersed in flint ; and, as far as 

 can be judged by a polished section at right angles to its surfaces, it 

 is very similar in its structure to our recent specimen of sponge, and 

 there is a total absence of the sinuous outline that would be exhibited 

 by a similar section of a specimen of Mantell's Ventriculites radiatus. 



DESCRIPTION OF THE PLATES. 

 Plate XLVI. 



Geodia carinata, Bowerbank. 

 Fig. 1 represents the type specimen of the species surrounding the remains of 

 the stem of a large Oorgonia, natural size. 



2. Three of the multiangulated cylindrical spicula from the dermal mem- 



brane, magnified 530 linear. 



3. One of the attenuato-spinulate skeleton-spicula, magnified 123 linear. 



4. A fully developed aborescent subsphero-stellate retentive spiculum from 



the interstitial membranes, magnified 530 linear. 

 5 represents one of the ovaria, magnified 250 linear. 



Geodia imperfecta, Bowerbank. 



Fig. 6 represents the type specimen, parasitical on Oculina rosea, natural size. 



7. An average-sized subfusiformi-acerate skeleton-spiculum, magnified 



80 linear. 



8, 9, 10, 11. Varieties of the undeveloped or malformed attenuato-patento- 



ternate connecting spicula, magnified 80 linear. 



