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of sponges in the English Chalk. As the preservation of 

 these spicules depends so much upon their capacity to resist 

 the eroding influences of fossilization which adversely affects 

 the minuter forms far more than the larger, too much stress 

 cannot be laid upon a calculation of the relative abundance 

 of the different orders of sponges, from the spicules which 

 have escaped destruction. To some extent the great number 

 of species ol the Tetractinellid sponges, which are more nume- 

 rous in this material than those of the other orders put to- 

 gether, may be due to the fact that the zone and body spicules 

 of this order are unusually robust, and would thus be more 

 likely to be preserved than the smaller spicules of other 

 sponges. But even allowing for this, the Tetractinellid sponges 

 appear to have predominated, and next to them the Lithistids 

 and. Hexactinellids are in about equal numbers, whilst the 

 Moiiactinellids, so far as can be determined, are few and un- 

 important. It may perhaps be deemed improbable that such 

 a number and variety of sponges should be mingled together 

 in such a small quantity of material but similar instances of 

 the occurrence of great numbers of sponges together have 

 also been discovered in modern deep - sea dredgings. Thus 

 for example; Sir W. Thomson records that in one haul of the 

 dredge in the North Atlantic there were brought up fort>- 

 specimens of vitreous sponges (An. Mag. Nat. Hist. 1869, 

 p. 119) and now lately, in material from the Gulf of Manaar 

 in the Indian Ocean which in quantity would hardly fill a 

 quart measure; Mr. Carter has described no fewer than 62 

 species of .sponge (An. Mag. N. H. S. 5, Vol. 6, p. 457); 

 so that the contents of this chalk-flint are to some extent pa- 

 rallelled by the deposits of the present oceans. 



It is doubtful whether any precise conclusions as to the 

 depth of the ocean in which these chalk sponges existed, 

 can be drawn from comparing tliem with existing sponges 

 whose bathymetrical limits have been ascrtaincd, on account of 

 the great limitswithin which sponges of the same genus oftentimes 



