61 
T-XP LA NATION OF PLATES 41, 42 
transverse ribs of the outer shell are strengthened 
by repeated intersections of the subjacent edges of 
the transverse Plates. (Original.) 
'g- 3. Back view of Ammonites sphmricus, from the 
•mestone of Derbyshire, shewing the position of 
le siphuncle upon the dorsal margin, with its collar 
advancing outwards between the two simple dorsal 
lobes ; the lateral lobes are also simple and with- 
out foliations, and pointed inwards. (Martin Pet 
Der. T. 7.) 
P’g. 4 Ammonites nodosus (Ceratites). This Is one of 
the species peculiar to the Muschel Kalk. The de- 
scending lobes terminate in a few small denticula- 
tions, pointed inwards, and the ascending saddles 
are rounded outwards, after the normal character of 
Ammonites. (Zeiten. Tab. II. Fig. 1. a.) 
Pig. 5. Back of A. Nodosus, shewing the dorsal lobes 
pointed inwards, and the collar around the siphuncle 
advancing outwards. No edges of the transverse 
plates are placed beneath the dome-shaped Tuber- 
cles; these derive sufficient strength from their 
vaulted form. (Zeiten. Tab. II. Fig. 1. b.) 
Plate 41. V. I. p. 349. 
^ Ammonites giganteus, found in the Portland stone at 
le +• Wiltshire. This beautiful fossil is in the col- 
th Miss Benett. The chambers are all void, and 
e transverse Plates and Shell converted to Chalcedony. 
^^r>ginal.) 
Plate 42. V. I. pp. 350, 351. Note. 
‘b- 1- Cast of a single chamber of Nautilus hexagonus, 
shewing the simple curvatures of the edges of the 
transverse plates, and the place of the Siphuncle. 
(Original.) 
