16 



lamella, hand-higli, 5-8 mm. thick and folded in the middle like the cover of 

 a book. The two elongated halves, which nearly touch each other, are each about 

 6 cm. broad and 9 cm. high. The fold (back of the book-co- r) is 5 cm. long 

 and 2 cm. thick. The longer free lateral margins of the two lamellae are on the 

 whole parallel to the fold, but have an undulating outline. The lamellte thin 

 out towards the margin, the edge of which, with the marginal spicules, has been 

 lost. The traces of the marginalia left are hardly visible to the naked eye. 

 There is no sharp limit between this lateral and the upper margin, into which 

 it gradually passes. The latter is convex, and also bears marginalia. The upper 

 margins of the two lamelte are divided at the fold by a pretty deep notch. The 

 lower margin of each lamella is the rough line along which it has been torn oft 

 from the basal part of the sponge. 



The lamellfe are covered on their external surface by a fairly even, velvet-like 

 dermal layer, the reticular structure of which is very indistinct. The inner, 

 gastral surface is more even and velvet-like than the outer. It is slightly reticu- 

 late and somewhat transparent, so that the excurrent canals lying below can be 

 seen through it. 



Some smaller fragments of identical spiculation, and therefore doubtless 

 belono-ing to the same species, were found not far off, 7° 34' 30" N., 76° 8' 28" E. 

 in a depth of 1530m.=836 fths. 



These consist of thin lamellae firmly pressed together, with irregularly torn 

 lateral margins. Their external surfaces are still covered in places by the finely- 

 reticulate dermal membrane. 



The supporting skeleton of the interior •chiefly consists of parenchymal 

 oxydiactine macroscleres. These are straight or slightly curved, smooth, and 

 gradually attenuated towards the pointed ends. Most of them are aggregated in 

 loose bundles which form a network traversing the sponge in every direction. Some 

 are isolated. They are 6-20 a^ thick and on an average 1-2 mm. long, occasion- 

 ally they attain a length of 6 mm. and more. Some have a ring-shaped thicken- 

 in o- or low protuberances, two opposite ones or four arranged crosswise, in the 

 centre. As a rule however such thickenings are absent. Some of the radial rays 

 of the stout subdermal and subgastral oxypentactines, which are up to 1 mm. 

 long, also take part in the formation of the supporting skeleton. 



Oxyhexactine microscleres with smooth rays of medium thickness, recurved 

 in the distal third of their length (pi. XIX, f. 8), are numerous in the 

 parenchyme. These spicules measin-e 80-120, usually 100 m in diameter. It is to 

 be noted that the oxyhexactines are not only scattered irregularly throughout the 

 whole of the parenchyme, but congregate in great numbers in the walls of the sub- 

 dermal cavities and the incurrent canals originating from them, where they often 

 occupy a radial position like true canalaria (pi. XIX, f . 2j. This circumstance has 



