71 
AMMONITES Greenoughi. 
TAB. CXXXIL 
Spec. Char. Depressed, volutions two-thirds con- 
cealed, obscurely undulated ; aperture elliptical, 
deeply indented by the preceding whorl. 
w horls four or live, the last nearly half the diameter 
of the shell, the undulations are continued and rather 
strongest over the rounding back, they are obscure in 
all but the central whorls, and the latter whorls of old 
shells are destitute of them. The outline of the aperture 
is a very regular ellipsis. The septa are near, very 
much and beautifully sinuated at their margins, and 
locked into each other. 
This rather singular Ammonite is often formed of 
pyrites, of rich golden and iridescent tints, and crystal- 
lized in the greatest variety of forms, from the oc- 
taedron to the icosaedron, following the undulations of 
the chambers and the most attenuated ramifications of 
the spreading follicuhe, sometimes forming in the place 
of the shells, &c. &c. occasionally filled with a great 
variety of crystals of Carbonate of Lime an inch or more 
in length. Specimens vary in size from 12 to 18 inches 
or even more. The outer whorl has generally few or no 
undulations, while they are more distinct in the center 
which, if seen separated, might be mistaken for an- 
other species. The attenuated and ramifying sutures 
of the septa are remarkably striking in the present spe- 
cimen, and put me in mind of the friendly and attentive 
