138 Mr. H. J. Carter on Fossil Sponge-spicules of 



Eetnming to the habitat of the deep-sea sponges and the 

 Coralliospongiffi respectively, we observe that they occasion- 

 ally mingle ; but while the former are chiefly confined to the 

 most retired depths of the ocean, the habitat of the latter tends 

 in the opposite direction. 



Xot only, however, do the deep-sea sponges and the Coral- 

 liospongiaB mingle, but there is one of the Pachytragiaj, viz. 

 Stelletta ( Tisiphonia) agariciformis^ Sdt., = Wi/ville-Thomsonia 

 WaUichiiy Wright, which exists on a reef in the Gulf of 

 Florida, in 178 fathoms, and Avas happily recognized by Dr. 

 Wallich in " soundings " of the Atlantic Ocean brought up 

 from a depth of 1913 fathoms. 



All honour, then, be to one who, so far back as " October 

 1860," secured this little, wee young specimen, not more than 

 l-12th of an inch in diameter (Quart. Journal. Microscop. 

 Sc. No. 37, Jan. 1870, pi. 2. fig. 1) for the futm-e advance- 

 ment of our department of science ! It has even been suggested 

 to me by Dr. Gray (to whose kind assistance much of this 

 communication is due), and not without reason, that Tethya 

 rimricata^ Bk. (Brit. Spong. vol. i. p. 25, and figs. 304 and 305), 

 may probably be the same sponge. 



Lastly, I would add that Schmidt (Atlant. Spong. Faun. 

 1870, p. 20, Taf. 2. figs. 16-20) reproduces several figm-es 

 from fossil remains in the Cretaceous system, which, from their 

 triaxial and "lattice-form" characters, he associates with the 

 living species of '■'• Farrea^Aplirocallisies^^ccADactylocahjx.'''' 

 And, as far as the minute triaxial or hexradiate spicules go, 

 he is right in considering them allied to these genera ; but when 

 instances of the silicified fibre are given as evidence of the 

 " hexradiate " plan of their structm'es generally, it will be seen, 

 as our figm*es show, that this is any thing but regular, and 

 that the teniate division of the large spicules of the circum- 

 ference, which alone we have had for our guidance, is the most 

 constant plan, and the one least subject to complex modification. 



The hexradiate form of the minute spicules answers 

 very well for the character of Schmidt's general grouping 

 under the term " Hexactinellida ;" but when we come to 

 divide the Sponges of the deep sea from the Coralliospongise, 

 other definitions are required ; hence the acceptableness of 

 Mr. Kent's term of " Calycispongias " for most of the former. 

 The remains of such sponges may be found in those deposits of 

 the Cretaceous system which, from their subtleness, may be 

 assumed to have been formed in deep seas, but not in such 

 as bear the characters of the Haldon deposit. 



Not so with the Coccoliths of the deep sea (to me calca- 

 reous, solitary, unicellular Algai), which so abound in the 



