( 20 ) 
hinge ; whether this is natural or accidental to the petrifaction cannot be decided, 
for no other example is known amonst the various species which have been found ; 
fig. 34 is a Hippurite, with a gutter, a, and a siphon, b; its surface is smooth and 
the septa are concave: fig. 33 is one of the most singular species which have yet 
been discovered ; the operculum is entire, and pierced with two eyes; it is only 
six lines in depth and fifteen in diameter: fig. 18, pl. 2, found in a considerable bed 
on the mountain of Montferrand is sometimes a foot and a half long, the diameter 
not exceeding an inch; the operculum has been destroyed by long exposure; M. 
de la Peyrouse observes, that their situation in the rock clearly indicates that they 
have been petrified in the same position and in the same place in which they had 
originated. De novis quibusdam Orthoceratitum et Ostracitum speciebus Dissertatiun- 
cula, Erlange, 1700. Dr. Thomson, formerly Professor of Anatomy at Oxford, saw 
several species in the cabinet of M. Chiarelli, at Palermo, in 1789, in the form of 
the femur of a cow or horse, which had been found entire at Cape Passora (the 
ancient Pachynus), with no bones whatever in their neighbourhood. Dr. Thomson, 
on visiting the spot expressly, could only meet with species in the form of a case or 
sheath, and equal in dimension to the horn of a bull about three years old; the 
interior hollow, and containing two cylindrical bodies, like two candles. The base 
of this cone is closed by a species of lid, similar to that of a powder hern. The 
internal structure resembles a heap of egg shells, broken transversely, and piled 
up so as to touch each other, but leaving a void space in the middle. These plates 
are so flexible that they allow the concave part of the horn to bend inwards when 
squeezed. Their disposition has some resémblance to the diaphragm of the human 
body. The Hippurite, therefore, is not entirely divided into concamerations, and has __ 
no tubes of communication, or siphons, as we find in the Ammonites, Belemnites, 
and Orthoceratites. The texture of this case, as it exists in a fossil state, is scaly 
lengthwise and across. The transversal fracture, when it is fresh, appears to be 
strong, and composed of concentric layers; but after having been some time ex- 
posed to the air, this fracture appears rotten and spongy, so that in the part 
changed by the air, it becomes ramified like an animal substance, which gives it 
the appearance of a bone. This fossil case is closed by an operculum, the internal 
surface of which is imbricated in converging rays, like the shell of the Pecten. 
The thickness of the operculum led Dr. Thomson to conclude that this case was 
inhabited by one animal only, and that it was not the nest of several. 
DIVISION V. LITUACER. 
GENERA. 
4. Lirovs. Breynius. 
The last turn elongated. 
a, Lituites, Mont. Turns contiguous. Pl. 1, 
fig. 7. 
b. Hortolus, Mont/. Turns separated, Pl. 1, © China: Foss. in the 
fig. 32. red limestone of Oeland ; 
Meudon ; in the limestone 
at Namur. 
2. Scapuires. Parkinson. 
The last turn (after bemg In the London lCay ; 
enlarged and elongated) Crag Marl; Melbury 
diminished and reflected Marble. 
inwards. Pl. 2, fig. 6. 
