HYALASCUS SIMILIS. lOl 



4063) and is now to be seen in the British Museum. It came 

 from the Sagami Sea, the more exact locality being unknown. 



The thick plate-like fragment is nearly as large as the blade 

 of a tennis racket. Greatest length, 480 mm. Greatest breadth, 

 255 mm. Thickness, 45 mm. It is torn all around, had evidently 

 been flattened out during desiccation and does not warrant in- 

 ference as to the shape and size of the original sponge except 

 that it must have formed part of the wall of a very large and 

 presumably vase-like individual. The piece, being preserved in 

 the dry state, is light and of a cavernous appearance on account 

 of broad incurrent and excurrent canals. The spongy septa 

 between the two canal systems are rather thick. The incurrent 

 canals, which in places may be 15 mm. wide, seem to freely 

 anastomose with their branches, thus forming a continuous system 

 extending throughout the whole specimen, while the excurrent 

 canals only occasionally intercommunicate with the branches and 

 more usually remain separate from one another. 



The dermal surface (PL VIII., fig. 3) is much macerated, so 

 that its exact nature is difficult to determine. Here and there 

 the apertures of incurrent canals appear as oval or roundish 

 openings of not over 10 mm. diameter. Not that they are all 

 freely open, Init a large number of them are seen to be covered 

 over with an uneven and irregularly cobweb-like layer formed of 

 spicular bundles which intersect, unite and branch in quite an 

 indefinite manner. The thicker bundles may show in places a 

 thickness of over 1 mm. Between the canalar apertures the said 

 layer is indistinguishable from the tissue of the parenchymal 

 septa. It is not to be doubted that tlie layer constitutes the 

 hypodermal framework. The dermal layer proper remains in 

 small patches only in a few places. Even if it were extensively 



