CEPHALOPODA. 11 
ORDER—TETRABRANCHIATA. 
Familyj—AMMONITIDE. 
Ammonites, Brugiere. 1789. 
OpuropomoRPHITEs, Plott. 
PLANORBITES, ORBULITES, GLOBITES, PLANULITES, Lam. 
AmALtTHEUS, PLanutitEes, De Montfort. 
PLANITES, GLopitEs, De Haan. 
Nautiius, Arconauta, Reinecke. 
AMMONITA, ORBULITA (pars.), Fleming. 
A more or less discoidal, multilocular shell, with contiguous volutions; volutions 
generally visible, septa transverse, with sinuated edges, perforated by a single tube, situated 
close to the outer margin. 
AmMonitEs sus-contractus. Plate II, figs. 1, la, jun., figs. 2, 2a. 
A, Testé discoided, subglobosd, costatd, umbilicatd, anfractibus involutis, rotundatis 
compressis, lateribus 16—18 costatis, costis obtusis bi-trifurcatis, in dorsum continuis ; 
apertura semiellipticad subcontractd ; umbilico magno, excavato, subconica. 
A sub-globose, deeply umbilicated, and costated shell, with sixteen to eighteen obtuse 
ridges (tubercles?) surrounding the margin of the umbilical cavity, from each of which 
three or four smaller costa pass over the somewhat depressed and rounded back. 
Aperture, semi-elliptical. 
Proportion of umbilicus to diameter, rather more than one-half. Diameter, 5 inches. 
Thickness, 3 inches. Height of aperture, 13 inches, twice as wide as it is high. 
The specimen from which our figure is taken has been much worn by clearmg it 
from the original matrix, but a careful examination discloses the prominent marginal coste, 
as well as the smaller ones which arise from them and pass over the back. 
In the umbilicus, the marginal costz are well exhibited, which in the young state were 
more compressed, and continued on the inner side of the cavity. 
This species is distinguished from the Ammon. coronatus, Brug., by its more globose 
form, less conical umbilicus, and the more arched and less expanded aperture. It is closely 
allied to Am. contractus, Sow., and in a young state might be mistaken for that species ; 
but the ribs are larger and not so numerous or elevated ; the less embracing volutions, and 
the more contracted form of the aperture in the adult shell, are also characters by which it 
may be distinguished. 
Unfortunately the determination of the species, and their varieties of the Ammonites in 
the Great Oolite of Minchinhampton, is rendered extremely difficult, in consequence of the 
great rarity of specimens, and their state of preservation, rarely allowing the least trace of 
the sinuated edges of the septa to be observed. 
