Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/750

 Phylloceras Capitanei, Catullo. Middle Lias.

— Nilsoni, Heb. Upper Lias.

— connectens, Zitt. Inferior Dogger.

— heterophylloides, Opp. Middle Dogger.

— disputabile, Zitt. Upper Dogger and Kelloway group.

— Demidoffi, Rouss. Of uncertain age (Crimea).

— Manfredi, Opp. Oxford group.

— Puschi, Opp. Oxford group.

— benacense, Cat. Aspidoceras-acanthicum beds.

— Kochi, Opp. Tithonian.

3. Series of Phylloceras ultramontanum. — Kneed radial furrows ; striae of shell entirely wanting, or only next to the outer side, and then coarse and short ; lobes and saddles clumsy ; first lateral saddle of the inner side with two-leaved termination. Species : — -

Phylloceras ultramontanum, Zitt. Inferior Dogger.

— Zignodianum, D'Orb. Middle Dogger.

— mediterraneum, sp. n. Klaus beds and Inferior Tithonian.

— polyolcum, Ben. Aspidoceras-acanthicum beds.

— silesiacum, Opp. Tithonian.

— Calypso, D'Orb. (=?P. berriasense, D'Orb.). Neocomian.

4. Series of Phylloceras tatricum. — Rounded prominence on the external side ; radial striation very faint, or entirely deficient ; saddles clumsy, first lateral saddle on the internal side (?). Species : —

Phylloceras tatricum, Pusch. Inferior Dogger.

— flabellatum, sp. n. Klaus beds.

— Hommairei, D'Orb. Age uncertain (Crimea).

— euphyllum, Neum. Kelloway and Oxford groups.

— ptychoicum, Quenst. Tithonian.

— semisulcatum, D'Orb. Neocomian.

5. Isolated types.

Phylloceras subobtusum, Kud. Klaus beds.

— viator, D'Orb, Oxford group ?

— Beneckei, Zitt. Tithonian.

— haloricum, Hauer. Klaus beds.

— tortisulcatum, D'Orb. Klaus beds and Tithonian.

The first three of these isolated forms, together with P. Rouyanum, D'Orb., from the Neocomian, may perhaps constitute a distinct series.

Each mutation within a series of forms presents very slight but constant differences, without any gradual transitions. The whole of the forms of a series may be considered either to belong to a single species, or to be specifically distinct. The last course seems to be best adapted for geological purposes ; and the genetic connexion may be indicated by adding to the name of the altered form that of the form from which it has been derived, under the algebraic symbol ____, as proposed by Waagen.

The objections against these distinctions as representing varities rather than genuine species, may be of weight as regards existing forms, or extinct forms within a given horizon, considered independently of any succeeding or preceding formation ; but in the whole chain of successive organisms the species extends into a series