TUTE: SINGULAR CAVITIES IN THE MAGNESIAN LIMESTONE. 183 
end being perfect), f of an inch in longest width, in shorter 
widtli. It is sHghtly arcnate longitudinally, and has an oval or 
rather ovate section transversely, the convex edge being more flatly 
rounded than the other. Between the cast and the investing matrix 
there is a slight space, which appears to have been originally occupied 
by the walls of the tube. A similar fossil has occurred in the Shell 
and Compact Limestone of Durham, agreeing in most respects with the 
one described." 
The casts in the Wormald Green Limestone agree generally with 
tin's description. They are more distinctly arcuate in the more 
perfect specimens ; straighter in the shorter ones ; and occasionally 
appear to spring from an irregularly formed base, which is coloured 
brown with iron oxide. The internal cast where it exists is formed 
of small rounded grains of limestone, slightly cemented together, but 
the tubes are more commonly only partially filled. 
Associated with them in the limestone we find Myalina haus- 
manni, some small gasteropods" and other shellsf which from the 
pliable nature of the deposit are difficult to make out. 
The animal which inhabited these cavities may have had habits 
similar to the common Lob-worm of our present shores, which 
Nicholson in his Manual of Zoologyf describes as living " in deep 
canals, which it hollows out in the sand of the sea-shore, literally 
eating its way as it proceeds, and passing the sand through the ali- 
mentary canal, so as to extract from it any nutriment which it may 
contain." 
I showed the quarry and these organisms to Mr. Richard Howse, 
the Curator of the Newcastle Museum. He kindly lent me Mr. 
Kirkby's paper, from which I have taken the foregoing extract. And 
afterwards he wrote to me saying, " since my return to Newcastle, I 
have, I think, made out from Dr. Geinitz' ' Dyas' a little about the 
doubtful organism you kindly showed me in the Wormald Green 
Quarry, I have also got two specimens from our Middle and Lowest 
Limestone, which I shall forward for your examination next week, 
and hope they will satisfy you that the organisms are the same as 
Litorina helicina. f Edmondia elougata. Bakewellia antiqua. 
tp. 222. 
