REPORT ON THE DEEP-SEA EERATOSA. 33 



differentiated skeletal fibres, the supporting skeleton being represented by foreign 

 enclosures lying separately in the parenchyma, and the secretion of the horny substance 

 having been reduced to the formation of only a thin envelope around the enclosed 

 foreign bodies." In contradiction to this description, the figure of Psammopemma, given 

 by Polejaeff, exhibits no trace of a horny envelope, but the xenophya are imbedded 

 immediately in the maltha or the so-called parenchyma of the mesoderm, in the same 

 way as the flagellated chambers. The same is the case in the original specimens of 

 Psammopemma densum, upon which Marshall founded the genus, and which he received 

 from my museum at Jena. A re-examination of them has convinced me that Marshall's 

 description is quite correct, and that there is no trace of spongin in the body, as Polejaeff 

 supposes. The "horny envelopes" described by the latter are the usual sheaths of 

 xenophya, or the condensed parts of the maltha, which envelop all the foreign bodies in 

 the ground-niass of the connective tissue. But if his Psammopemma porosum really 

 possesses "fully-developed horny envelopes around the foreign enclosures, occasionally 

 with very conspicuous outgrowths," then probably this species should be transferred to 

 Cerelasma (p. 45), or to an alhed genus of Spongebdse. 



The Psamrninidae often seem to inhabit the deep sea, and during the ten years in 

 which I made my investigations on the Challenger Eadiolaria, I found in many soundings 

 from the Challenger collection irregularly formed lumps or crusts, which a closer 

 examination proved to be fragments of arenaceous Keratosa without horny fibres. But 

 only seven of these Psainniinidse were preserved in a manner sufficient for their descrip- 

 tion as new species. In two of these seven deep-sea Psamminidse the pseudo-skeleton 

 is composed of Radiolarian ooze ; in four others of Globigerina ooze ; in another it is 

 built up of red clay. It therefore seems probable that all the different kinds of deep- 

 sea bottom are accidentally employed by several Myxospongise for the construction of a 

 pseudo-skeleton. 



The external appearance of all these Psamminidse is generally simple and insignificant, 

 the general form being an irregular lump or crust ; at first sight one is inclined to regard 

 them as porous lumps of inorganic deposit. But anatomical examination, especially by 

 means of sections through different planes, shows that the sandy body is traversed by 

 branched canals, which are in connection with flagellated chambers, the characteristic 

 organs of sponges. 



Canal-System. — The state of preservation of the deep-sea Psamminidse which I 

 found in the Challenger collection was usually not sufficient to enable one to recognise 

 its true structure with precision ; besides, their examination is very difficult, owing to 

 the dense sand masses which fill up the whole mesoderm. In four cases, however, I 

 succeeded in recognising the main parts of the canal-system, and convinced myself that 

 it is constructed on the Leuconal-type. This was recognisable in those four species of 

 Psamminidse in which the pseudo-skeleton is composed of agglutinated Globigerina 



(zool. chall. exp. — part lxxxii. — 1889.) Nnnn 5 



