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 ot 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 
Monactinellids, 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 forty 
specimens of vitreous sponges (An. Mag. Nat. Hist. 13869, 
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, NN.’ H: S; 53. Vol6;)'p. 457)3 
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 them with existing sponges 
whose bathymetrical limits have been ascertained, on account of 
the great limits within which sponges of the same genus oftentimes 
