Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/976

 ture, which he regards as increased by the employment of two or more specific denominations. To get rid of this difficulty, and introduce a system which, he thinks, would be expressive of the relations of many forms, he proposes to introduce after the generic name the radical sign ( y' ), placing beneath it the name of the fundamental specific form, and above it that of the form supposed to be derived from this by "mutation." Thus the designation (or, as the author calls it, " the genetic formula ") of Ammonites biflexuosus (D'Orb.)

biflexuosus, D'Orb. would be as follows : — Ammonites subradia- subradiatus, Sow.

tus being the fundamental form, and biflexuosus the form derived from it by " mutation."

Dr. Waagen also proposes to divide the genus Ammonites into several genera and subgenera, according to the length of the chamber occupied by the animal, the form of the mouth, the presence or absence of the operculum and its nature when present (Aptychus or Anaptychus), and the sculpture, — the outlines of the lobes being regarded as furnishing only secondary characters, and the general form as of scarcely any importance. The groups founded by him upon the consideration of these characters are the following : —

Genus I. AEgoceras (Capricorni, von Buch, commencing in the Muschelkalk with Amm. incultus, Beyr., and including A. planorbis, angulatus, planicosta, &c).

Genus II. Arietites (the group Arietes, best represented by A. Bucklandi).

Genus III. Amaltheus, Montf. (commencing in the Muschelkalk with Amm. megalodiscus, Beyr., and including as Jurassic forms A. Guibalianus, oxynotus, margaritatus, pustulatus, cordatus, Lamberti, &c).

Genus IV. Harpoceras (Falciferi, Flexuosi, von Buch, Insignes, Disci, Denticulati, &c), with 3 subgenera : —

1. Harpocerassens. str. (Liassic Falciferi, Insignes: forms like A. canaliculatus, trimarginatus, &c).

2. Oppelia (Flexuosi and Tenuilobati : A. subradiatus, A. psilodiscus and its allies).

3. OEkotraustes (forms allied to the Oppelioe, but with the body-chamber geniculate : A. genicularis, dentatus, macrotelus, &c).

Genus V. Stephanoceras (Coronati, Planulati, Macrocephali, and (?) Ornati), with 3 subgenera ; —

1. Stephanoceras sens. str. ( = Coronati and Macrocepali).

2. Perisphinctes ( = Planulati).

3. Kosmoceras ( = Ornati).

Genus VI. Aspidoceras (including A. perarmatus, bispinosus, cyclotus, &c). [Count M.]

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