EXPLANATION OF PLATES 41. 42.
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transverse ribs of the outer shell are strengthened by repeated intersections of the subjacent edges of the transverse Plates. (Original.)
Fig. 3. Back view of Ammonites sphæricus, from the limestone of Derbyshire, showing the position of the siphuncle upon the dorsal margin, with its collar advancing outwards between the two simple dorsal lobes; the lateral lobes are also simple and without foliations, and pointed inwards. (Martin Pet. Der. T. 7.)
Fig. 4. Ammonites nodosus (Ceratites). This is one of the species peculiar to the Muschel-kalk. The descending lobes terminate in a few small denticulations, pointed inwards, and the ascending saddles are rounded outwards, after the normal character of Ammonites. (Zeiten. Tab. II. Fig. 1. a.)
Fig. 5. Back of A. Nodosus, showing 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 Tubercles; these derive sufficient strength from their vaulted form. (Zeiten. Tab. II. Fig. 1. b.)
Plate 41. V. I. p. 264.
Ammonites giganteus, found in the Portland stone at Tisbury in Wiltshire. This beautiful fossil is in the collection of Miss Benett. The chambers are all void, and the transverse Plates and Shell converted to Calcedony. (Original.)
Plate 42. V. I. pp. 264, 265. Note.
Fig. 1. Cast of a single chamber of Nautilus hexagon us, showing the simple curvatures of the edges of the transverse plates, and the place of the Siphuncle. (Original.)
