4 Air. W. J. Sollas on Stauronema^ a new 



distance above it, the maximum distance I have measured 

 being 5 inch. 



Asj then, the normal distal margin has not been seen in a 

 single specimen, one is miable to say how much further it 

 originally extended : it may have terminated close to its 

 present level, though, from the abrupt way in which it is 

 fractured, it more probably reached some distance above ; or it 

 may have been continued into a large flabelliform expansion, 

 thinning away above and many times larger in area than the 

 portion now remaining — in which case this plate would be 

 the really essential sponge, and our fossil merely its base 

 overgrown with the posterior mass ; and the probability of 

 this view derives support from the fact that I have in my 

 possession a thin plate of fossil sponge (PL I. fig. 9), 



5 inches long by 4 broad, and from -i- to yV inch thick, 

 curved from side to side, and exhibiting, as we shall see 

 presently, every structural peculiarity to be found in the an- 

 terior plate of our fossil. Whether this is really a continua- 

 tion of the anterior plate can only be demonstrated by finding 

 a specimen in which the latter actually passes into such a 

 flabelliform expansion ; and for such a one I have directed Mr. 

 Griffiths, of Folkestone, to make a search. 



The front face of the anterior plate is a plain surface as far 

 as the level of the posterior protuberance ; but beyond this, 

 where it begins to project freely, it is marked by a number of 

 round, or more usually oval, oscular pits arranged quincun- 

 cially (PI. I. fig. 1), and on the whole constant in size 

 and distance from one another in the same specimen, but 

 differing in both these respects in different specimens 

 (PI. I. figs. 1 & 3). The variations in size may all be 

 comprised between the extremes of ^ and -^ inch for the 

 length of the major axis of the ellipse. 



The posterior face is of course covered below by the posterior 

 mass ; but above, where it is exposed, it generally exhibits a 

 number of oval spaces arranged quincuncially and closely re- 

 sembling the oscular pits in front (PI. I. figs. 2 & 8), a 

 little less regularity in arrangement and a thickening of the 

 intervening structure into irregular ridges in the case of the 

 posterior markings constituting the only difference, and that 

 not a constant one, between the two. Sometimes the free 

 posterior face is smooth, like the lower part of the anterior 

 face. 



When the anterior plate is broken across, one may see the 

 oscules of its anterior face prolonged into cylindrical tubes, 

 which pass inwards normal to the surface, and, receiving irre- 

 gular lateral canals in their course, terminate in the oval spaces 



