54 THE VOYAGE OF H.M.S. CHALLENGER. 



between Stannophyllum and the other species of Psammophyllum, which in structure 

 approach more to Sp>ongelia. 



Family IV. S t a n n o m i d m, n. fam. (Pis. I. -III.). 



Definition, — Keratosa with a fibrillar spongin-skeleton composed of thin, simple or 

 branched, spongin-fibrillse, never anastomosing or reticulated. Pseudo-skeleton com- 

 posed of xenophya (or diverse foreign bodies), which are crowded in the transparent 

 maltha, never in the homogeneous fibrillse. Canal-system vesicular, developed on the 

 Leuconal-type (similar to that of the Spongelidse). 



The new and most remarkable family Stannomidse comprises those Keratosa 

 hitherto unknown, which produce true horny fibrillse in the mesoderm, and besides possess 

 a pseudo-skeleton composed of various xenophya ; but these foreign bodies are enclosed in 

 the clear maltha or the ground-mass of the connective tissue, not in the spongin-fibres 

 (as in the Spongelidae), All Stannomidse are inhabitants of the deep sea ; they are very 

 dissimilar in external form, while they all agree in internal structure. Three different 

 types of external form may be distinguished, viz.— (l) Stannophyllum, with foliaceous 

 or laminar flabellate body (Pis. I., II.) ; (2) Stannarium, with a branched body, 

 composed of several free or coalescent foliaceous wings (PI. III. figs. 6-14) ; and (3) 

 Stannoma, with a branched arborescent or coralliform body, the branches of which are 

 cylindrical, either free or connected by anastomoses (PL III. figs. 1-5). The size of 

 these two latter Stannomidse is usually between 30 and 60 mm., while the large flabelli- 

 form leafs of Stannophyllum reach a diameter of 100 to 200 mm. and more. 



The Stannomidse discovered by the Challenger have all been found in the central part 

 of the Tropical Pacific, in depths between 2425 and 2925 fathoms. The majority of the 

 specimens collected were taken at Station 271, in the equatorial central Pacific (depth, 

 2425 fathoms) ; some other forms were captured in the neighbouring Stations 270 and 

 272. The Stannomidse are the most important and most interesting of all the Keratosa 

 collected by the Challenger. Their structure is so strange and so peculiar that several 

 distinguished spongiologists, to whom they were submitted for investigation, said they 

 were not sponges. Some naturalists declared that they were gigantic Rhizopods. 

 Nevertheless I am now quite convinced that they are true horny sponges ; some new 

 forms of Psammophyllum (Pis. IV., V.), which form an uninterrupted continuous series of 

 modifications and connecting links between Stannophyllum and Spongelia (Phyllo- 

 spongia), leave no room for doubt. 



Unfortunately, the state of preservation of all the Stannomidss collected, as well as of 

 the peculiar Hydroida living in symbiosis with them, was very imperfect, and not 

 sufficient for the examination of the finer structures. It is natural that " these delicate 

 things, drawn up rapidly through the water from a depth of nearly four statute miles, 



