20 DR. J. S. BOWER3A.MK ON THE SPONGIAD.E. [Jan. 7, 



fibres, forming a rather regular elongate reticulation ; and the same 

 mode of fibrous arrangement prevails on the bulbous surface of the 

 sponge, but not with quite so much regularity in its structure. Be- 

 neath the fibrous stratum at the dermal surface, the sponge is prin- 

 cipally composed of a mass of interstitial reticulate skeleton-struc- 

 ture, with a few long threads of spiculo-fibrous tissue running amidst 

 it. The reticulate interstitial skeleton-structure is uniform and re- 

 gular in its construction, the rete being unispiculous, and the areas 

 rarely exceeding the breadth of the length of one spiculum ; the 

 spicula are of the same size and form in all parts of the sponge. 



There is a considerable amount of similarity in form and structure 

 between this Australian species and our British one, Desmacidon 

 Jeffreysii. Both are bulbous in form, and they are both furnished 

 with long fistulous cloacae ; but those of D. fistulosa are very mucli 

 more delicate in their structure than the similar organs in D. Jef- 

 freysii ; and in the latter species there are large root-like basal pro- 

 cesses which serve to elevate the sponge above the mass to which it 

 may have been attached ; but no such organs appear to have existed 

 in D. fistulosa. The spicula in both sponges are exactly alike in 

 size and form, but they do not agree in their mode of arrangement. 

 In the dermal membrane of D. Jeffreysii they appear always to as- 

 sume more or less of a reticulate arrangement ; but in the like organ 

 of D. fistulosa they are irregularly dispersed. The interstitial ha- 

 lichondroid part of the skeleton in both species also differs. In D. 

 fistulosa it is very delicate and the rete is unispiculous, while in D. 

 Jeffreysii the rete is often constructed of two or three spicula, and 

 the areas are much larger and more irregular in their construction. 

 In these structural characters there are therefore good and sufficient 

 specific differences to discriminate the species. It is an interesting 

 fact, but by no means a singular case, that we should have a fossil 

 sponge from the hard chalk of Flamborough closely resembling 

 the recent specimen, D. fistulosa, from Australia. This fossil 

 sponge is described by Mr. John Edward Lee in Charlesworth's 

 'Magazine of Natural History,' vol. iii. for 1839, p. 15, as Spongia 

 spinosa, and is represented in page 1G, figs. 11 and 12 ; and I have 

 by me a specimen of the same species of fossil from the locality men- 

 tioned by Mr. Lee, which is much more like the recent D. fistulosa 

 than the specimens described and figured by that author. Not only 

 does the fossil resemble the recent sponge in its external characters, 

 but there is little doubt that in its living state its internal struc- 

 ture was also similar. Mr. Lee, in page Ifi of his paper, writes, 

 " Being anxious to see more of the internal structure, I had the spe- 

 cimen cut through just below the plates figured in the last diagram : 

 an irregular fibrous structure then became visible, similar to that 

 shown in fig. 12." The artist, in the figure of the specimen thus 

 treated (13), has faithfully represented the fibrous structure alluded 

 to, on each side of the lower part of the figure ; and the fibrous struc- 

 ture is so like that in the corresponding part of the recent D. fis- 

 tulosa, that the drawing would equally well represent the arrange- 

 ment of the fibrous skeleton-tissues of either species. 



