REPORT ON THE DEEP-SEA KERATOSA. 19 



and the Spongelidse (Pis. IV.-VI.) ; it is quite absent in the two other families, the 

 Psamminidae (PI. VII.) and the Ammoconidaj (PI. VIII.). These two latter families 

 therefore are, strictly speaking, not Keratosa (or Ceraspongiae) but Malthosa (or Myxo- 

 spongise). The important question of the natural relations of these different groups will 

 be discussed in the Appendix. 



The Spongelidse of the deep sea are represented in the Challenger collection by two 

 genera, both differing essentially in the structure of the horny skeleton from the common 

 Spongelidse of shallow water. The stout and strong main fibres of the horny skeleton, 

 which form the solid scaffold of the body in these latter, are wanting in the former ; they 

 are replaced by the chitinous tubes of the symbiotic hydrorhiza. The spongin production 

 is restricted in Psammophyllum (Pis. IV., V.) to a framework of very thin branched 

 spongin fibres, forming a delicate network, which is expanded within the meshes of the 

 far stouter network produced by the symbiotic Hydroid. Psammophyllum seems to be 

 closely related to the similar Spongelid Phyllospongia pcvpyracea (Ehlers), but this 

 shallow-water form possesses the same stout main fibres as the common Spongelia. 



The other genus of deep-sea Spongelidse, Cerelasma (PL VI.), is distinguished from 

 all other genera by the peculiar form of the spongin secretion. The spongin here forms 

 peculiar capsular envelopes around the xenophya, and these are connected by branched 

 lamellae, which form a loose framework. The more solid reticular framework of the 

 symbiotic hydrorhiza branches everywhere between the meshes of the former, and gives 

 them a firm support. 



The new family Stannomidse (Pis. I.— III.), represented by numerous large forms, 

 forming the most stately portion of the collection here described, differ from all other 

 Keratosa in the peculiar development of the spongin-skeleton. This is composed of 

 innumerable fine yellow threads or fibrillar, which run in all directions through the meso- 

 dermal maltha, partly single, partly associated in bundles. They are usually simple and 

 very long, more rarely branched, and never anastomose. They never enclose xenophya, 

 but run everywhere around and between them. A closer examination shows that they 

 cannot be hyphse of fungi, or other foreign productions (as was supposed by some 

 naturalists), but that they agree perfectly in chemical nature and anatomical structure 

 with the finer horny fibres of the common Spongelidse. 



Xenophya. 1 — The foreign bodies which compose the pseudo-skeleton of the Deep- 

 sea Keratosa, and which we call briefly " xenophya," differ in composition according to 

 the nature of the bottom on which the living sponges grew. The young sponge naturally 

 takes for the building up of its supporting pseudo-skeleton the xenophya making up the 

 bottom at that locality. The three principal kinds of ooze usually found at the bottom 

 of the deep sea compose accordingly the xenophyal skeleton of our Keratosa, viz., 

 (l) Radiolarian ooze, (2) Globigerina ooze, and (3) red clay. Besides, the inorganic 



1 Xenophya = ^e>oil)vef, foreign bodies. 



