280 Mr. H. J. Carter on Jcnoivn Fossil Sponges. 



two (? or three) pairs of thin dental plates in the upper jaw, 

 the hinder pair attenuated mesially and not closelj apposed in 

 the median line ; lower dentition consisting of a pair of large 

 dental plates, meeting at the sjnipliysis, 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 ofhnoion Fossil Sponges in 

 Relation to those of the Present Day. By H. J. CARTER, 

 F.R.S. &c. 



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 Eas Abu Ashrin^ opposite the north-east end of the 

 Island of Masira (where there is a little '' bite ^' 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 

 eauvioi mixed up with sand, all of which had drifted into 

 this position (the result probably of many of the mon- 

 soons when the sea reached this ridge). Secondly, that 

 Dr. K. V. Lendenfeld, in his " Monograph on the Austra- 

 lian Sponges" (Proc. Linn. Soc. ^. S. Wales, voh ix. 

 pt. ii. p. 311), has stated that the horny sponge Aplysilla 

 vioJacea, L., " covers many thousand metres in Port 

 Phillip," and that of the 348 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 " 



