REPORT ON THE DEEP-SEA KERATOSA. 



61 



ment of spongin-fibrillse and the relatively smaller quantity of xenophya (for the most 

 part Radiolarian shells) which are disposed in the maltha between them. The fibrillse 

 are very much alike, and regularly arranged in thick crossed bundles (PI. II. fig. 2). 

 The leaf, therefore, is coriaceous, more elastic and coherent than in the four other species. 

 Its surface is soft and velvet-like, and marked by a number of distinct concentric zones, 

 which run parallel to the semicircular distal margin. 



The second species, Stannophyllum radiolarium (PI. I. fig. 2), connected with the 

 first by numerous intermediate forms, is composed almost entirely of Radiolarian shells ; 

 the spongin-fibrillse between them are scarce, very thin, of nearly equal breadth. The 

 leaf, therefore, is homogeneous, and in the dry state is like a thin plate of fine sand ; the 

 external surface is quite even, finely arenaceous, without zones and ribs. The physical 

 consistence is rather inelastic, stiff, and fragile. 



Whilst in these two species the pseudo-skeleton is composed mainly of siliceous 

 Radiolarian ooze, it consists in the third almost entirely of calcareous Globigerina ooze. 

 The spongin-fibrillse in the connecting maltha of this Stannophyllum globigerinum (PI. I. 

 fig. 5) are very unequal in size, many coarse and thick between the main mass of thin threads 

 which are irregularly interwoven in all directions like cotton threads. Usually they are 

 more fully developed in the softer medullar plate of the leaf, in which the network of 

 symbiontes expands between the canals of the sponge, and in which the smaller shells and 

 fragments of Globigerina are crowded ; whereas the two parallel porous dermal plates 

 contain only a small quantity of fibrillse, and are usually composed for the most part of 

 larger Globigerina shells. In consequence of this composition the leaf of this .species is 

 extremely flaccid and soft in the wet state, non-elastic, fragile and friable in the dry 

 state. The surface is coarsely granular or sandy, and exhibits sometimes (but not always) 

 indistinct concentric zones, like those of Stannophyllum zonarium ; with this species it 

 is connected by numerous intermediate forms (compare PI. I. figs. 1,5). 



The two remaining species, Stannophyllum venosum (PI. I. fig. 4) and Stannophyllum 

 pertusum (PI. I. fig. 3), appear in a certain sense as intermediate forms between Stanno- 

 phyllum globigerinum and Stannophyllum radiolarium. They are distinguished by the 

 possession of thick, prominent, branched ribs, which arise from the insertion of the basal 

 pedicle. These thick ribs are whitish, and composed mainly of Globigerina ooze, while 

 the thin brown membrane between them is supported by Radiolarian ooze ; the quality 

 and quantity, however, of these two different materials is very variable in the different 

 specimens of these two species, Stannophyllum venosum approaching generally nearer to 

 Stannophyllum globigerinum, and Stannophyllum pertusum to Stannophyllum radio- 

 larium. The spongin-fibrillse are in the two latter species more equal and delicate 

 than in the two former. Besides, Stannophyllum pertusum is characterised by the 

 presence of a great quantity of siliceous sponge spicules (mainly Hexactinellida), and 

 perhaps to this is due the greater fragility and flaccidity which characterises this species, 



