336 PARTS OF AN AMMONITE. 
Hence we infer that during the Secondary and 
Transition periods a more general distribution of 
the same species, than exists at present, pre- 
vailed in regions of the world most remotely 
distant from one another. 
An Ammonite, like a Nautilus, is composed of 
three essential parts: 1st. An external shell, 
usually of a flat discoidal form, and having its 
surface strengthened and ornamented with ribs 
(see PI. 35, and PI. 37.) 2nd. A series of internal 
air chambers formed by transverse plates, inter- 
secting the inner portion of the shell, (see PI. 36 
and 41). 3rd. A siphuncle, or pipe, commenc- 
ing at the bottom of the outer chamber, and 
thence passing through the entire series of air 
chambers to the innermost extremity of the shell, 
(see PI. 36, d. e. f. g. h. i.) In each of these 
parts, there are evidences of mechanism, and 
rebratulse, and other Bivalves, that occur in the English Oolite ; 
thereby establishing the existence of the Lias, and Oolite forma- 
tions in that elevated and distant region of the world. He has 
also collected in the same Mountains, shells of the genera Spirifer, 
Producta, and Terebratula, which occur in the Transition for- 
mations of Europe and America. 
The Greensand of New Jersey also contains Ammonites mixed 
with Hamites and Scaphites, as in the Greensand of England, 
and Captain Beechey and Lieutenant Belcher found Ammonites 
on the coast of Chili, in Lat. 36. S. in the Cliffs near Concep- 
tion ; a fragment of one of these Ammonites is preserved in the 
Museum of Hasler Hospital at Gosport. 
Mr. Sowerby possesses fossil shells from Brazil resembling those 
of the Inferior Oolite of England. 
