REPORT ON THE DEEP-SEA KERATOSA. 



49 



the canal-system and the maltha, partly by the network of the symbiotic Spongoxenia, 

 The horny lamellse are partly tubular, partly expanded in the form of thin Keratose 

 membranes. They are overladen with xenophya, in the same way as the granular maltha 

 (fig. 7). There are besides a great number of roundish black-brown pigment-cells scattered 

 in the maltha, so that its structure is difficult to make out. 



Xenophya. — -The majority of the foreign bodies in the maltha as well as in the 

 Keratose lamellse are broken siliceous spicules of different sponges ; between them are 

 scattered many fragments of Globigerina shells and mineral particles, more rarely single 

 tests of Radiolaria. Many xenophya possess peculiar yellow envelopes of spongin, whilst 

 others lie immediately in the transparent maltha (fig. 7). 



Symbiontes. — The tubular network of Spongoxenia is very differently developed in 

 the two specimens examined, in one very rich, in the other rather scarce. The anasto- 

 mosing chitinous tubes are of the same shape as in Stannophyllum, and belong probably 

 to Stylactella; they are filled with dark cellular detritus. 



Genus 8. Psammophyllum, 1 n. gen. 



Definition. — Spongelidse with foliaceous or flabellate body, supported by a network 

 of homogeneous spongin-fibres of nearly equal thickness, which enclose manifold xenophya. 

 Maltha clear, also often filled by xenophya. 



The genus Psammophyllum, represented in the Challenger collection by three deep- 

 sea species, is in the external foliaceous form very similar to the Stannomid Stannophyllum; 

 in internal structure it is closely allied to the typical Spongelia or Dysidea. It differs 

 from this latter in the flat leaf-like form of the body, which seems to be partly produced 

 by the flabelliform growth of the symbiotic Hydroids (Stylactella, Halisiphonia, &c.) 

 (cf. below). On the other hand, Psammophyllum seems to be nearly allied to 

 Phyllospongia papyracea, Ehlers ; from this, however, it differs essentially in the 

 absence of main-fibres and the structure of the skeleton (cf. above, p. 43). 



The three species of Psammophyllum, which are described in the following pages, were 

 taken in the Tropical and Northern Pacific (from depths between 2100 and 2900 fathoms), 

 and are of special importance ; they are very similar in external shape, but rather different 

 in internal structure. Psammophyllum annectens (PI. IV. figs. 1-4) is very similar to 

 Stannophyllum zonarium, and has similar thin spongin-fibrillge, but they exhibit 

 frequent ramifications and anastomoses, and begin to enclose xenophya. Psammophyllum 

 jlustraceum (PI. IV. figs. 5-9) is distinguished by much coarser spongin-fibres, of very 

 unequal thickness, many enclosing xenophya, as in Spongelia. It approaches more to 

 Psammophyllum reticulatum, in which the horny network is composed of scanty fine 



1 Psammophyllum = Sandy leaf, i^a^et, (pi/Xhov. 



(ZOOL. CHALL. EXP. PART LXXXII. — 1 889. ) Nllim 7 



