8 DR. J. S. BOWERBANK ON THE SPONGIADjE. [Jail. 7, 



there remains scarcely a trace of the dermal membrane or of the 

 sarcodous stratum immediately beneath it, and the greater portion of 

 the sarcode of the interior is also destroyed. A few minute external 

 defensive spicula were seen projecting from one portion when 

 sectioned for examination, and a few small fusiformi-acerate ones 

 lying parallel to the surface, apparently belonging to the membranous 

 tissue, being all that I could detect. In some of the depressions of the 

 surface of Dr. Fleming's specimen there are the remains of a very thin 

 parasitic sponge with spinulate spicula, which might readily be mis- 

 taken for a portion of the absent dermal membrane, while in truth 

 they have no organic connexion with the Geodia. 



The skeleton-spicula of this species, although similar in form to 

 those of G. zetlandica, differ exceedingly in size, the latter having 

 the average length of one eighth of an inch, while those of the 

 former rarely exceed one eighteenth of an inch in length. They are 

 slender in proportion, and intermingled with the fusiformi-acerate spi- 

 cula ; there are a very considerable proportion of purely acerate ones 

 exhibiting no tendency to the fusiform shape. The two forais of stel- 

 late spicula of the sarcode are indiscriminately mixed and dispersed in 

 that substance ; and the cylindro-stellate ones are very much the 

 smaller of the two, requiring a linear power of at least 600 to render 

 their forms visible ; their extreme diameter does not exceed 4 ^W 

 inch, while the attenuato-stellate ones vary from y&To mcn to vhi 

 inch in diameter. 



The spicula of the membranes are few in number, small, and in 

 many cases scarcely, if at all, fusiform. 



I did not observe any prolific or immature ovaria in the external 

 crust of the sponge ; but in the internal membranes they were in 

 every stage of development. The immature ones always appeared to 

 be completely surrounded by a thick coat of sarcode ; but this sar- 

 codous coat was not apparent in the fully developed ones. 



The spicula figured are from Dr. Fleming's specimen, from the 

 Island of Dominica. They are identical in all their structural 

 characters with those from the specimens in the French Museum in 

 my possession. 



Geodia perarmatus, Bowerbank. (Plate II.) 

 Sponge massive, sessile. Surface even. Oscula congregated in 

 depressed areas. Pores inconspicuous, dispersed. Dermal mem- 

 brane pellucid, spiculous ; tension-spicula fusiformi-acerate, minute, 

 short, rather few in number ; retentive spicula subsphero-stellate, 

 radii attenuating, rather obtusely terminated, very few in number, 

 and simple attenuato- or cylindro-stellate, very minute, abundant. 

 Skeleton-fasciculi compact ; spicula fusiformi-acerate, large and 

 stout. Connecting spicula attenuato-patenti-ternate with bifur- 

 cating radii, very large and stout ; and recurvo-ternate, small and 

 slender, shafts long and attenuated ; also porrecto-ternate, minute and 

 slender. Interstitial membranes — spicula the same as those of the 

 dermal membrane. Ovaria spheroidal, slightly depressed. 



Colour in the dried state cream-yellow. 



