280 Mr. H. J. Carter on known Fossil Sponges. 
two (? or three) pairs of thin dental plates in the upper jaw, 
the hinder pair attenuated mesially and not closely apposed in 
the median line; lower dentition consisting of a pair of large 
dental plates, meeting at the symphysis, and a median incisor- 
like tooth in front. A few dermal plates present upon the 
head; males with a large prehensile spine upon the snout. 
XXXVII.— Sketch of the History of known Fossil Sponges in 
ftelation to those of the Present Day. By H. J. Carter, 
F.R.S. &e. 
In this brief “ Sketch”? I propose to state my impressions 
as to the relation the species of fossil sponges that have 
been found bear to those which now exist, since in going 
over the former I have been forcibly struck with the total 
absence of any certain representatives of the horny sponges, 
whose toughness and durability combined with their great 
abundance would lead one to infer that at least they would 
be as likely to be handed down through fossilization as the 
elytra of insects. 
To give an idea of the abundance of existing horny sponges 
and their accumulation in certain localities favourable to future 
fossilization I may mention, first, that at the beginning of 1845, 
when I was attached as Medical Officer to the Survey of the 
South-east Coast of Arabia, I saw on the low sandy coast 
close to Ras Abu Ashrin, opposite the north-east end of the 
Island of Masira (where there is a little “ bite 7’ which receives 
the backwater of the current produced by the waves of the 
south-west monsoon as they rush by it to the mainland during 
this tempestuous season), a raised ridge, about 50 yards from 
the margin of the sea (then calm), covered, as I thought, 
with bushy plants, but which on examination proved to 
be large Keratophytes, horny sponges, and a host of other 
exuvie mixed up with sand, all ot which had drifted into 
this position (the result probably of many of the mon- 
soons when the sea reached this ridge). Secondly, that 
Dr. R. v. Lendenfeld, in his ‘ Monograph on the Austra- 
lian Sponges” (Proc. Linn. Soc. N. 8S. Wales, vol. ix. 
pt. 11. p. 811), has stated that the horny sponge Aplysilla 
violacea, L., ‘covers many thousand metres in Port 
Philip,” and that of the 3848 horny sponges from all 
parts of the world, which he has enumerated in his Mono- 
graph, 258 or 74:1 per cent. “ occur in the Australian seas ”’ 
