REPORT ON THE DEEP-SEA KERATOSA. 



53 



rather dense, composed of branched fibres of nearly equal thickness ; the majority of 

 the fibres without xenophya ; the thickest fibres enclose remains of Radiolaria, which also 

 fill up the maltha. 



Psammophyllum annectens has the same external appearance as Stannophyllum 

 zonarium (PI. I. fig. l); it is a broad reniform leaf, soft and thin, of a brown colour 

 with concentric zones on the surface. The height of the leaf (without pedicle) is usually 

 25 to 30 mm., breadth 35 to 40 mm., thickness 1 to 3 mm. The largest specimen, 

 however (figured in PI. IV. fig. 1), is 75 mm. broad, 55 mm. high, without the pedicle 

 (10 mm.). The concentric zones or bands of both surfaces, which run parallel to the 

 semicircular margin, have the same breadth as in the similar Stannophyllum zonarium, 

 3 to 4 mm. ; they are separated by superficial furrows, somewhat thicker on the proximal 

 than on the distal margin. The dried body is very soft and flexible, of felty appearance. 

 The inferior edge of the kidney-shaped leaf is more or less concave (in a smaller specimen 

 scarcely emarginated), and from its centre starts a short conical pedicle, with a small 

 basal plate for attachment. 



Canal-System. — The entire surface of the sponge on both sides of the leaf is covered 

 by a rather firm dermal membrane, and this is pierced by small inhalent pores ; between 

 them are scattered at irregular distances larger openings (two or three times the diameter 

 of the inhalent pores), probably the exhalent oscula ; these occur mainly on the proximal 

 margin of the concentric zones, which is somewhat thickened. The large subdermal 

 cavities, which occur in the similar Stan?iophyllum, are absent in this species. 



Symbiontes. — The whole spongy parenchyma of the leaf between the two dermal 

 plates is traversed by a network of cylindrical anastomosing tubes, the hydrorhiza of a 

 symbiotic Hydroid (Spongoxenia). Perhaps this is the same, Stylactella abyssicola, as 

 occurs in the similar Stannophyllum. I was able to find in one specimen the 

 hydranths and gonophores, which were not distinct in the latter (cf. PI. II. fig. 7). 



Xenophya. — The foreign bodies which compose the pseudo-skeleton in this species are 

 almost exclusively siliceous shells of numerous Radiolaria and their fragments, as in the 

 closely-allied species of Stannophyllum {radiolarium and zonarium). They fill up the 

 clear maltha of the mesoderm, and are connected, and partly enclosed, by the spongin- 

 fibrillse (PI. IV. figs. 2, 3,/). 



Horny Skeleton. — The spongin-fibrillse in this species are more like those of 

 Stannophyllum and those of the Stannomidse in general than in any other Spongelidse 

 hitherto known. They are very thin and of nearly equal breadth (0"003 to 0'006 mm. 

 on an average), but they differ from the simple fibrillse of the Stannomidee in the numer- 

 ous ramifications and anastomoses. The network thus formed includes the xenophya, 

 and the larger Radiolarian shells are surrounded by its meshes. Smaller shells and 

 fragments are also enclosed in the fibres, and they fill up the maltha between them 

 (PI. IV. fig. 2, r). Psammophyllum annectens, therefore, is a true intermediate form 



