REPORT ON THE DEEP-SEA KERATOSA. 



67 



Stannophyllum venosum, n. sp. (PL I. fig. 4). 



Habitat. — Station 271 ; depth, 2425 fathoms; bottom, Globigerina ooze. 



Sponge with a broad flabelliform or reniform leaf, in the basal incision of which a 

 stout and short pedicle is inserted. Distal margin semicircular, undulate and lobulate. 

 Surface distinctly veined, with numerous thick, whitish, branched ribs, which diverge 

 from the insertion of the pedicle ; between them thin, flabby, brown lamellae. In the ribs 

 the skeleton is composed mainly of calcareous Globigerina ooze, in the lamellse of siliceous 

 Radiolarian tests ; spongin-fibrilla? thick and coarse in the former, thin and fine in the 

 latter. , \ 



Stannophyllum venosum, represented in PL I. fig. 4 half natural size, is the largest of 

 all the Deep-sea Keratosa, the longitudinal diameter of the flabelliform leaf reaching 200 

 mm. and the transverse diameter 250 mm. It is distinguished at once from the other four 

 species of the genus by the strong, prominent, white ribs or veins arising divergently from 

 the insertion of the thick basal pedicle and tapering towards the thin lobulate margin. 

 The pseudo-skeleton of these thick whitish ribs is composed principally of calcareous 

 Globigerina ooze, while that of the thin yellowish or brown lamella? between them 

 consists for the most part of siliceous Radiolarian shells. The spongin-fibrillse are very 

 unequal in size, thicker and rather coarse in the ribs, thinner and finer in the lamellse 

 between them, the network formed by them being loose and irregular in the former, 

 denser and finer in the latter. 



External Form. — In the largest specimens there are seven of the peculiar thick veins or 

 branched ribs, which are prominent on the two faces of the thin flaccid leaf. In the middle 

 there is an odd rib, or a prolongation of the thick basal pedicle, and three divergent pairs 

 on each side, each rib being again branched or beset with secondary ribs. The tapering 

 distal ends of the branches pass gradually over into the thin brown web of the distal 

 portion of the leaf, which is very flabby and easily torn. The development of these ribs 

 seems to be produced partly by strong bundles of reticular symbiotic Hydroids, partly by 

 strong bundles of coarser spongin-fibrillse (0'006 to 0*01 mm. in diameter), strengthened 

 by crowded Globigerina ooze ; the thin brownish membrane between the thick whitish 

 ribs is composed mainly of Radiolarian tests and of thinner fibrillar (0*001 to 0'002 mm. 

 in diameter). 



The thick and short basal pedicle which is inserted into the proximal portion of the 

 reniform leaf is 20 to 30 mm. in length and 6 to 8 mm. in thickness. It is attached to 

 the sea-bottom by a basal plate, 15 to 20 mm. in diameter. The thickness of the 

 lamellar leaf diminishes gradually towards the very thin and flabby distal margin, which 

 is slightly undulate and lobulate ; sometimes the distal portion of the leaf is pierced by 

 small irregular holes, but neither these perforations nor the marginal lobes are so 

 pronounced as in the closely-allied Stannophyllum pertusum. 



