68 Havveij B. Hull — On Fossil Sponges. 



pressure being applied equally on all parts. Prof. Surs dredged 

 .sponges, actinozoa, true molluscs and worms at a depth of 800 I'atli- 

 oms, and the Swedish deep sea dredges, in the expedition to Spitzber- 

 gen, brought up crustacea, mollusca, and annelides at depths of from 

 0,000 to 8,400 feet. Quoted in the Intellectual Observer for Dec, 

 1866, p. 400, from Annals of Nat. History.] Moreover, some further 

 explanation will suggest itself when speaking of the sponges of Far- 

 ringdoD, and the manner in which fo.ssilization of the sponge appears 

 to have often taken place. 



Whether Polyzoa and other parasites are really more frequent on 

 the fossil than on the recent sponge, is a question I am not prepared to 

 answer. But M. De Fromentelle is certainly not correct in saying that 

 tliey never occur upon recent sponges; and very frequently the adhe- 

 sion of the parasites to the fossil sponge is more apparent than real, 

 being produced solely by the cementing influence of fossilization, and 

 by the nature of the matrix in which they are imbedde<l. In any case, 

 unless the Polyzoa grew upon dead individuals, the nature of the 

 skeleton could have had no influence upon the parasite, as, whatever 

 it may have been, it was equally invested by the sarcode of the animal. 

 That the serpulre and ostreidte sometimes become attached to the 

 sp )nge while living is apparent from their having become partially 

 embedded in the sponge tissue which has grown over them ; but it is so 

 also with recent sponges : and as regards the worn appearance of the 

 parasites and other foreign bodies occasionally found attached to the 

 sponge, it is quite possible that they may have undergone attrition be- 

 fore they became adherent ; and, moreover, the fossil itself may have 

 been derived from jn-e-existing deposits, as were the Oalitic forms 

 found in the gravels of Farringdon. 



But there is, in fact, no real ground for assuming with D'Orbigny 

 and others that the skeleton of the fossil sponges was necessarily always 

 solid and resisting, like that of the recent Dadylocahjx, Stucth, the 

 Farrea of Bowerb., etc. Many of the siliceous sponges no doubt were 

 so ; but as regards the calcareous ones it may be observed that among 

 recent species, according to Bowerbankj "carbonate of lime, as an 

 •elem.ent of the skeleton, is known only in the form of spicula." h\ 

 some cases, as will be shown hereafter, the fibers or twigs were origi- 

 nally complex, formed of bundles of spicula, like the twigs in many 

 of the recent species, and were afterward consolidated more or less 

 • completely by the fossilizing process. But there is no evidence that 

 in others it may not have been keratose, either with or without the 

 •accessory spicuja. Some of our recent horny sponges are not less resist- 

 .ant than the solid siliceous fibrous species, and are certainly less fria- 



