( 20 ) 



hinge ; whether this is natural or accidental to the petrifaction cannot he decided, 

 for no other example is known amonst the various species which have been found ; 

 fig. 31 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, pi. 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 qulbusdam Orthoceratitum et Ostracitum speciebus Dissertatiun- 

 cula, Erlangse, 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 horn. 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 resemblance to the diaphragm of the human 

 body. The Hippurite, therefore, is noi 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. LITUACEJEI. 



GENERA. 



1. Irrruus. Brejnius. 

 The last turn elongated. 



a. L'ituif Montf. 



b. Hortolus, Montf. 



2. Scaphites. Parkinson. 



The last turn (after being 

 enlarged and elongated) 

 diminished and reflected 

 inwards. PL 2, fig. 6. 



Turns contiguous. PI. 1, 

 fig. 7. 



Turns separated. PI. 1, 

 fig. 32. 



China : Foss. in the 

 red limestone of Oeland ; 

 Meudon ; in the limestone 

 at Namur. 



In the London iCay ; 

 Crag Marl; Melbury 

 Marble. 



