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W. J. Sollas — A New Cretaceous Sponge. 



intersect them. Those fibres which ascend from ' A ' to a, or 

 from ' B ' to h, cross right over the top of the sponge and join 

 ' C ' in the former, or ' D ' in the latter case, on the opposite side of 

 the sponge. 



Diagram-plan of the fibres in Eubrochus clausus. 



If this were all, it would happen that as the curving fibres diverged 

 from one another, the spaces between them would continually enlarge, 

 and the meshes of the net would get bigger and bigger the further 

 they were from the basal centres. This, however, is prevented by 

 the appearance, wherever the divergence has become considerable, 

 of fresh fibres (PL XIV. Fig. 3 a, and woodcut), and thus -the 

 meshes are kept of tolerably constant size. 



The younger fibres so introduced are of less diameter than the 

 primary ones, as is shown by the fact that their casts do not score 

 so deeply into the coprolite, hence the fibres would seem to have 

 grown thicker with age. 



The characters we have just described are quite sufficient by 

 themselves to distinguish the sponge, and I now propose the name 

 Euhrochus clausus for it ; Eubrochus on account of its fine meshwork, 

 and clausus because its interior cavity is quite closed. 



With a view to making out the internal structure of Euhrochus, 

 the broken face of the fragment in the Woodwardian Museum was 

 carefully ground down and polished several times, so as to obtain 

 sections at different depths. When examined with a one-inch 

 objective by reflected light, patches of lattice-like tissue and sex- 

 radiate knots were to be seen here and there in the matrix, but no 

 regular and continuous network like that which appears on the 

 exterior. From this one could not decide whether the sponge pos- 

 sessed any other skeleton in addition to the single layer of meshwork 

 which forms its dermal reticulation, since the few fragments of sex- 

 radiate structure observed in the interior might possibly have been 

 washed in from without during the process of fossilization ; in order, 

 therefore, to determine this point, I obtained nermission to cut 



