TRANSLATIONS AND NOTICES
OF
GEOLOGICAL MEMOIRS.
1. Phylloceras in the Jurassic Series. By Dr. M. Neumayer.
[Imperial Geological Institute, Vienna, June 30, 1871. ]
The abundance of species of this genus is a palaeontological characteristic of the Mediterranean Jurassic rocks, their occurrence being comparatively rare in those of the neighbouring middle European region. In any well-known deposit containing these Cephalopods, four chief types of Phylloceras may be distinguished ; the representatives brought together from all horizons constitute four great series of forms, besides which a few isolated species occur. The members of each series, nearest in geological age, present a striking mutual affinity, although the differences between them, accumulating in the same direction, produce a considerable discrepancy between the oldest and the youngest forms. In the first place, the sutural line is continuously modified in one direction, the division and complication of the sellar leaves gradually increasing. Analogous, but less important, modifications take place also in the sculpture of the shell ; but very little regularity is noticeable in the modifications of the general form, transverse section, &c.
The four series of forms distinguished by the author are as follows : —
1. Series of Phylloceras heterophyllum. — Sculpture of shell only simple radial striae or folds; saddles slender, nearly symmetrical ; termination of the first lateral saddle of the inner side one-leafed. The species of this series are : —
Phylloceras heterophyllum, Sow. Upper Lias.
— trifoliatum, sp. n., Inferior Dogger.
— Kudernatschi, Hauer. Klaus beds.
— Kunthi, sp. n. Kelloway group.
— plicatum, sp. n. Oxford group.
— isotypum, Ben. Aspidoceras-acanthicum beds.
— saxonicum, sp. n. Ibid.
— serum, Opp. Tithonian.
— ptychostoma, Ben. Ibid.
— Thetis, D' Orb. Neocomian.
— ?velledae, Mich. Gault.
2. Series of Phylloceras Capitanei. — Internal cast with simple furrows inclined forward, corresponding to prominences (never to furrows) of the shell ; distinct radial striae, bending forwards ; saddles slender, unsymmetrical ; first lateral lobe of the inner side with a two-leaved termination. Species : —
VOL. XXVII. PART II. B
