rLACOSO^rV PAr.ADlfTYUM. / 



places tliey lie tolerably close together. The thin and soft oscular 

 rim is as often as not slightly raised in a lip-like manner. The 

 oscnla lead either directly into deep going excnrrent canals or 

 into such spaces of the excurrent canal-system as lie covered over 

 by only a thin layer of the pith-like sponge-tissue. More than 

 one secondary osculum may open into such a superficial space. 

 This should not be mistaken for a subdermal space ; the thin 

 layer over it represents the entire thickness of the sponge-wall, 

 consisting, as it does, of parenchymalia in addition to the dermal 

 layer. If we suppose a number of oscnla to have opened through 

 it in close proximity to one another, we should have a structure 

 strictly comparable to the Euplectellid sieve-plate. I believe it 

 contains the chamber-layer in an undulating disposition, in much 

 the same way as we usually see it in the thin marginal rim of 

 cup-shaped Hexactinellids ; all the chambers, I think, have 

 apopyles directed away from the external surface and towards the 

 canalar space mentioned above. But this point could not be de- 

 finitely ascertained by direct observation, on account of the 

 desiccated state of the specimen. 



80 far as the outward appearance goes, there is a certain 

 resemblance between the back-surface of the present species and 

 the gastral surface of certain other Hexactinellids, the oscnla of 

 the former simulating the apertures of excurrent canals opening 

 on the latter. But, from the mode of origin of the gastral 

 cavity, there should constantly exist an essential difference in 

 the relation of the dermal and scastral surfaces to the outer or 

 the inner aspect of the chamber-layer. In the case of a real 

 gastral surface, the apopylar ends of chambers should invariably 

 be turned towards it, — not away from it, as they should be if 

 the surface were dermaL. 



