SUPPLEMENT 
A MONOGRAPH 
OF THE 
MOLLUSCA FROM THE GREAT OOLITE. 
CEPHALOPODA. 
Ammonites Butuatus, D’Orbiy. Tab. XXXI, fig. 1. 
Ammonites BuLtatus, D’Orb. Pal. Fr. Ter. Jurass., p. 412, pl. 142, figs. 1 and 2. 
— — Kiidernatsch. Abhand. K. K. Geol. Reich., 1 band., taf. iii, 
figs. 1—4—11. 
—_ PLATYSTOMUS, Quenst.? Cephal., t. 15, fig. 3. 
— Buuiatus, Oppel. Juraform., p. 549. 
_ — Quenstedt.? Der Jura., t. 64, fig. 13, p. 479. 
Testa bullatd, irregulari ; anfractibus subinvolutis, latis, ultimo angustato, transversim 
late costato ; costis inequalibus; apertura constrictd, semilunari. (D’Orbigny.) 
Shell inflated, globose, variable in form throughout all the stages of its growth, orna- 
mented with large, transverse, slightly elevated ribs, which pass from the umbilicus over 
the back to the other side, not straight, but curved forwards; these are separated by other 
shorter ribs, which alternate with the larger series of ribs in the adult state, but in the 
young state there are two and sometimes three short ribs between each of the longer 
ones. ‘The volutions of the spire are irregular and embracing, forming a contracted um- 
bilicus in the young state; subsequently the volutions are less contracted, which renders 
the shell unsymmetrical or deformed. ‘The back is rounded, the mouth much contracted 
and prolonged in the middle part. The septa are very much complicated. 
In England this Ammonite is very rare. ‘The aged example figured is seven inches in 
