The Medals of Creation, Volumes 1 and 2 / First Lessons in Geology and the Study of Organic Remains

by Gideon Algernon Mantell

Aptychus, Meyer. (Trigonellites, Parkinson.) [Lign. 165].—Associated with the remains of Ammonites in several localities, are found flattened triangular bodies, from less than an inch to an inch and a half in diameter, the nature of which is still somewhat problematical. A good figure is given by Mr. Parkinson of one species (Org. Rem. vol. iii. pl. xiii. figs. 9, 10, 12. See Pict. Atlas), with the name Trigonellites latus. These bodies frequently occur in pairs and in apposition, as in the specimen figured in [Lign. 165]. Their structure is cellular; one surface is slightly concave and striated, and the other covered with minute circular pores. Altogether their appearance is that of bodies enclosed in vascular integuments. It is supposed that they are the opercula of Ammonites. These fossils are commonly found in the last or body chamber of Ammonites, in the Oxford Clay, near Chippenham, the Coral Oolite of Malton, the Lias of Lyme Regis, and the lithographic limestone of Solenhofen. M. Ewald states that they may be found in the Chalk Scaphites by making a longitudinal section of the body chamber: but I have not succeeded in detecting them in the examples from the chalk-marl which I have broken up for that purpose. As these bodies (alluded to by authors as Trigonellites, Aptychus, Munsteria, &c.) will probably come under the observation of the collector, especially among the fossils of the Kimmeridge Clay, these remarks are introduced to suggest diligent research, in the hope that the origin of these fossils may at length be discovered.

---

DISTRIBUTION OF FOSSIL CEPHALOPODA.

Geological Distribution of Fossil Cephalopoda.—Even from this short review of the principal types of the fossil Cephalopoda, the great interest which attaches to the study of this class of organic remains is strikingly demonstrated. Their geological distribution is alike replete with phenomena of an important character. In the Lower Palæozoic (Lower and Upper Silurian) strata, the chambered mollusks belong (with a very few doubtful exceptions) to the Nautilidæ, namely, Nautilus, Lituites, Cyrtoceras, Orthoceras, &c. The Devonian and Carboniferous systems contain Nautilus, Clymenia, Gyroceras, Cyrtoceras, and Orthoceras, together with a peculiar group of Ammonitidæ, the Goniatites. The Trias in general is extremely poor in Cephalopoda; the Permian group affording but two species of Nautilus, and the Muschelkalk two other species: but, in addition to these, the Muschelkalk contains Ceratites, which is a genus peculiar to the Triassic group, and chiefly abounds in the St. Cassian beds (in the Austrian Alps), where it is accompanied by Nautilus, Orthoceras, Ammonites, and Goniatites. In the Lias and Oolite Nautili abound, and we meet for the first time with Belemnites. The same families, viz. Nautilidæ, Ammonitidæ, and Belemnitidæ, prevail throughout the Cretaceous strata. The Tertiary formations contain a few Nautilidæ only; no vestiges of the Ammonitidæ and true Belemnitidæ, which, as we have seen, swarmed in the ancient seas, are perceptible, while in the existing oceans, the Nautilus and Spirula are the sole representatives of the numerous shell-bearing cephalopoda of the ancient geological eras. Thus, the Nautilidæ extend from the oldest to the newest fossiliferous strata, the genus being still in existence: the Ammonitidæ, on the other hand, though less ancient in origin, do not pass beyond the limits of the cretaceous epoch.

In the following tabular arrangement these facts are placed in a more distinct point of view:—

Tabular View of the Distribution of Cephalopoda through the Geological Epochs.

Existing Genera		Argonauta. Octopus, &c.		Octopoda.				Dibranchiata.
		Loligo, Cranchia. Sepiola, Onychoteuthis, &c.		(Teuthidæ).		Decapoda.
		Sepia (Sepiadæ).
		Spirula.
		Nautilus (Nautilidæ). Tetrabranchiata.
General fossil in the Tertiary Formations		Sepiadæ		Sepia, Spirulirostra, Beloptera, Belemnosis.
		Nautilidæ		Nautilus and Aturia
Cretaceous Deposits		Belemnitidæ		Belemnites, Belemnitella, and Conoteuthis.
		Nautilidæ		Nautilus.
		Ammonitidæ		Ammonites, Crioceras, Scaphites, Ancyloceras, Toxoceras, Hamites. Ptychoceras, Helicoceras, Turrilites, Baculites.
Oolite and Lias		Sepiadæ		Sepia.
		Teuthidæ		Teudopsis, Beloteuthis, Geoteuthis, Leptoteuthis, Ommastrephes.
		Belemnitidæ		Belemnites. Acanthoteuthis, and Belemnoteuthis.
		Nautilidæ		Nautilus.
		Ammonitidæ		Ammonites, Ancyloceras.
Trias		Nautilidæ		Nautilus.
		Ammonitidæ[427]		Ammonites, Goniatites, and Ceratites.
Carboniferous System		Nautilidæ		Nautilus, Gyroceras, Cyrtoceras, Gomphoceras, and Orthoceras, Actinoceras, &c.
		Ammonitidæ		Goniatites.
Devonian System		Nautilidæ		Nautilus, Clymenia, Cyrtoceras, Phragmoceras, Gomphoceras, Orthoceras, Actinoceras, &c.
		Ammonitidæ		Goniatites.
Upper and Lower Silurian Systems		Nautilidæ		Nautilus, Lituites, Gyroceras, Cyrtoceras, Phragmoceras, Gomphoceras, Oncoceras, Ascoceras, Orthoceras, Actinoceras, &c.

[427] The Ammonitidæ are from the St. Cassian beds only.