| Fig. | 1.— | Goniatites Listeri. |
| 2.— | Goniatites striatus. | |
| 3.— | Outline of a suture of Goniatite. | |
| 4.— | Outline of a suture of Ammonites venustus. | |
| The Arrows in figs. 3 and 4 denote the direction of the dorsal line. | ||
GONIATITES. CERATITES. CRIOCERAS.
Goniatites, [Lign. 159].—From the numerous family of Ammonites, a separation has been made of a large division, in which the margins of the septa are not deeply notched or foliated, and are destitute of lateral crenatures or denticulations, so that their outline always presents a continued uninterrupted line. The siphuncle is relatively small. The last or outer cell of the shell extends beyond one turn of the chambered part. The back is occasionally keeled, but in most species is round. In illustration of this genus, which is named Goniatites, I have selected two common species ([Lign. 159]) from the Carboniferous limestone, and annexed outlines of a suture (the edge of the septum) of a Goniatite, and of an Ammonite, for comparison. The importance of the separation of this type of Ammonites into a distinct genus, relates to the Goniatites being restricted to some of the older sedimentary strata; for although there are sixty British species, none of them have been observed above the Carboniferous system.[419]
[419] G. Henslowi, G. striatus, and G. sphæricus, are figured in Bd. pl. xl.
In Ceratites the sutures are more simple than in the Ammonite, being lobed rather than foliated; and the alternate lobes have their edge crenulated or finely toothed. (C. nodosus, Bd. pl. xl.) This genus is found in the Muschelkalk and the Keuper formations of Europe and Asia.
Our limits will not permit us to extend this notice of the very numerous family of Ammonitidæ,[420] except to offer a few illustrations of some of the modifications in form to which we have already alluded, and which will assist the student in discriminating these fossil remains.
[420] For further information, Dr. Buckland’s Treatise, and the respective articles in the Penny Cyclopædia, may be referred to. Mr. Woodward’s Manual should be consulted for the classification of the family, and M. D’Orbigny’s Paléontologie Française for the illustration of species.
Crioceras (coiled-horn), [Lign. 160], fig. 2.—This shell differs from the Ammonites in the turns of the spire being distant from each other. The siphuncle is continuous, and the septa are regularly divided into six lobes. I have found specimens of this genus in the Chalk-marl at Hamsey, and in the White Chalk, near Lewes (Foss. South D. tab. xxiii. fig. 9).
