COPROLITES. 195 
brane, by which it was lined. This evidence 
consists in a series of vascular impressions and 
corrugations on the surface of the Coprolite, 
which it could only have received during its 
passage through the windings of this flat tube.* 
Specimens thus marked are engraved at PI. 15, 
Figs. 3, 5, 7, 10, 12, 13, 14. 
If we attempt to discover a final cause for 
these curious provisions in the bowels of the 
extinct reptile inhabitants of the seas of a 
former world, we shall find it to be the same 
that explains the existence of a similar structure 
a coprolite, from the inferior chalk, in which this involute 
conical form is well defined. Fig. 4, is the transverse section 
of another Coprolite from the lias, showing the manner in which 
the plate coils round itself, till it terminates externally in a 
broken edge, at (b). In all the figures the letter b, marks the 
transverse section of this plate, where it is broken off near the 
termination of its outer coil ; the sections at b, show also the 
size and form of the flattened passage through the interior of the 
screw. 
A lamina of tenacious plastic substance pressed continually 
forwards from the interior of such a screw, into the cavity of 
the large intestine, would coil up spirally within it, until it 
attained the largest size admitted by its diameter ; from this coil 
successive portions would be broken off abruptly, at (b,) and 
descending into the cloaca would be thence discharged into the 
sea. 
* These impressions cannot have been derived from the mem- 
brane of the inferior large intestine, because they are continued 
along those surfaces of the inner coils of the Coprolite, which 
became permanently covered by its outer coils, in the act of 
passing from the spiral tube into this large intestine. 
