Fig. 6. Siphuncle of an orthoceratite (related to Orthoceras duplex, of Kissinger), from the Silurian strata, Sweden.
Fig. 7. An Orthoceratite (O. pyriforme, of Sowerby), from the Silurian strata, Dudley.
Figs. 8-15. Various kinds of Belemnites.
In the "[Supplementary Notes]" I have, under the head, "Belemnites," explained somewhat fully the nature of those fossils which, by the name of "thunderbolts," have for so many centuries excited the interest and perplexed the ingenuity of collectors of fossil remains. Referring the reader to that note, I shall therefore in this place merely give such specific names of the specimens figured by Mr. Parkinson as I have been able to determine.
Fig. 8. "A Belemnite of large size," Mr. Parkinson. This specimen is part of the phragmocone from near the lower apical portion, partially invested with the fibrous rostrum or guard. It is the species named Belemnites giganteus by M. D'Orbigny; from the Oxford clay of Wiltshire.
Fig. 9. The guard of a Belemnite, eroded by some Annelide.
Fig. 10, is a vertical section of a fragment of a Belemnite, showing the alveolus or cavity for the reception of the apex of the phragmocone in the upper part.
Fig. 11. The distal or apical part of the rostrum or guard of a Belemnite. The annexed outline of a transverse section exhibits the radiated structure.
Fig. 12. The distal part of the guard of a chalk Belemnite (Belemnitella mucronata); from Norwich. Siliceous casts of the phragmocone of Belemnitella are occasionally met with in the flints of the South Downs. This phragmocone has a longitudinal flat band or ridge, extending down the dorsal aspect: the chambers are very numerous; the slit or fissure in the ventral aspect of the guard, is occupied by a thin expansion of the phragmocone.
Fig. 13. A Belemnite from the great oolite of Stonesfield (Belemnites fusiformis, of Parkinson). The upper part shows the alveolus for the reception of the apex of the phragmocone.