SINUOUS EDGES OE TRANSVERSE PLATES. 347 
‘^urve, into a variety of attenuated ramifications 
undulating sutures. (See PI. 38. and PI. 
•^7, Figs. 6, 8). Nothing can be more beau- 
fifiil than the sinuous windings of these sutures 
many species, at their union with the exterior 
shell; adorning it with a succession of most 
S'l'aceful forms, resembling festoons of foliage, 
'^tid elegant embroidery. When these thin septa 
^*'6 converted into iron pyrites, their edges ap- 
pear like golden filigrane work, meandering 
fiinid the pellucid spar, that fills the chambers 
the shell.* 
* The A. Hetcropliyllus, PI. (38), is so called from the appa- 
lent Occurrence of two different forms of foliage; its laws of 
'Isntation are the same as in other Ammonites, but the ascending 
®®condary saddles (PI. 38. S. S.) which, in all Ammonites are 
“"ound, are in this species longer them ordinary, and catch attention 
^ore than the descending points of the lobes, (PI. 38. d. 1.) 
The figures of the edge of one transverse plate are repeated in 
®ach successive plate. The animal, as it enlarged its shell, thus 
having behind it a new chamber, more capacious than the 
hst, so that the edges of the plates never interfere or become 
Entangled. 
Although the pattern on the surface of this Ammonite is 
^Pparently so complicated, the number of transverse plates is 
but 
sixteen in one revolution of the shell ; in this, as in almost 
^ I other cases, the extreme beauty and elegance of the foliations 
^‘^sult from the repetition, at regular intervals, of one symme- 
oal system of forms, viz. those presented by the external 
i^argin of a single transverse plate. No trace of these foliations 
®een on the outer surface of the external shell. (See 
■ 38, c.) 
^ The figures of A. obtusiis, (PI. 35 and PI. 36), shew the rela- 
oiis between the external shell and the internal transverse par- 
