1872.] DR. J. S. BOWERBANK ON SPONGIAD/E. 201 



of the diaphragm was always outward, so that when viewed from 

 within it presented a slightly funnel-shaped depression, the bottom 

 or wnicli was conical. 



A section at right angles to its surface of one of the diaphragms 

 mounted in Canada balsam measured ^ of an inch in tffi 

 being ; at least eight or ten times that oFSfe lining membrane rfS 

 canty The recurvo-ternate spicula always accompany the expando- 

 ternate ones ; but their grapnel-like heads rarely appear to reach the 

 nner surface of the dermal crust, and I did not observe in any case 

 that their heads were immersed in the stratum of gemmules The 

 recurved radii of these spicula are remarkably long* Occasionally! 

 but very rarely, a porrecto-ternate spiculum was found anion- the 

 recurvo-ternate ones. among ine 



The skeleton-spicula are large and stout ; they were collected in 



X" f T mU0US faSC u iCUli mUnin S fr0m the basal centre to the 

 sur ace of the sponge, where they unite with the attenuated shafts 

 of the connecting spicula. The cylindro-stellate spicula of the sar- 

 code of the interstitial membranes are in great abundance ; they are 

 precisely the same in form and size as those immediately beneath 

 the dermal membrane. The gemmules, or ovaria, in the dermal 

 crust are mostly fa, an exhausted or solid state ; oc asionally onThe 

 outer surf of th st there are a fw . n a 7 on the 



Thev a re also abuudantly dispersed over the interstitial membrane 

 of the interior, and in that part of the sponge the greater number of 

 prolific ones are to be found. They may be There seen in all decree 

 alwtrT ent; th *J?™8°** im P e ' fe <% developed ones app«r 

 « I 7 I °^% SUrr0Unded b / a P r °P er mem brane, within whichThev 

 are embedded ma mass of pulpy or sarcodous matter. Considering 

 the foramen to be the top of the gemmule, their form is that of a 

 sphere considerably depressed, so that viewed in profile they present 

 quite an oval form. The diameter of an adult'one measured wa 



The anatomy of this remarkable species exhibits an amount of 

 elaborate structural peculiarities that could scarcely be imTS to 



2 "f cVeSTei^ 6 rt ° C0QSldered t0 bC am °^ he loweft in^ 



DESCRIPTION OF THE PLATES. 



Plate X. 



Geodia M* Andrew ii, Bowerbank. 



Fig. 1. Resents the type specimen, half the natural size, in its present dned 



^ % A n2?80 llr ° f th6 krge fu8ifo — ate defensive spicula, mag . 

 Rg ' 3 ' ^OW^ P ° rrect °- ternate exte ™ al defensive spiculum, magnified 



Fig. 4. One of the large attenuated porrecto-furcated ternate external defensive 

 spicula, magnified 80 linear. utiensive 



F lg . 5. A minute subspinous cylindro-stellate spiculum from the dermal mem 

 brane of one of the porous areas, magnified 530 linear. 



