214 
AMMONITES concavus. 
TAB. XCIV.— Lower figure. 
Spec. Cuar. Involute depressed, keeled, umbilicate ; 
umbilicus a large hemtspherical depression ; 
volutions four, concave near the centre; radii 
numerous, curved, unequal in length, obsolete 
near the centre; keel sharp, entire; aperture 
acutely triangular; external angle rounded ; 
internal angles obliquely truncate. 
EE, ee 
Aperture half the diameter of the shell, with the sides 
rounded, approaching to parallel; the radii, which are 
very conspicuous over half the whorl, are alternately long 
and short, the longer ones often continue, but obscurely, to 
the centre, the others sometimes join into them. The thick- 
ness is one-sixth of the diameter. The shell not very thin. 
This general form and undulating character of the costa 
is not very rare, but the peculiarity of a regularly concave 
centre is a convenient distinction at present. ‘This is not a 
rare species in the neighborhood of Ilminster, and I have 
had some larger ones long since by favor of the Rev. Dr. 
Sutton of Norwich. Specimens generally consist of nearly 
transparent Carbonate of Lime, more or less covered with 
an ochraceous marle; the one I have figured is filled with 
granular Limestone. 
