138 Mr. H. J, Carter on Fossil S^ionge-spicides of 



Returning to the habitat of th-e deep-sea sponges and the 

 Coralliospongiaj 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 opjiosite direction. 



Not only, however, do the deep-sea sponges and the Coral- 

 lios])ongia3 mingle, but there is one of the Pachytragia;, viz. 

 Stelletta ( Tisiphoma) ar/ariciformis, Sdt., = Wyville-Thomsonia 

 Walh'chii, Wright, which exists on a reef in the Gulf of 

 Florida, in 178 fathoms, and was 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 ■ 

 1-1 2th 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 Tethi/a 

 vna-icafa, 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 figures 

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

 triaxialand "lattice-form" characters, he associates with the 

 living sjjecies of '^ Farrea,A_i)IirocaUistes, and Dacfz/Iocalyx.^^ 

 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 structures generally, it will be seen, 

 as our figures show, that this is any thing but regular, and 

 that the ternatc 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 " Ilexactinellidffi ;" but when we come to 

 divide the Sponges of the deep sea from the Coralliospongia3, 

 other definitions are required ; hence the acceptableness of 

 My. Kent's term of " Calycispongia^ " 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 Alga;), which so abound in the 



