On the Fossiliferous Development of the Zone of Ammonites angulatus , Schloth., in Great Britain

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Abstract
I. I ntroduction . T he beds comprised between the Avicula-contorta series and the limestones of the zone of Ammonites Bucklandi vel bisulcatus have been divided into two lithological horizons, the lower of which, that of Ammonites planorbis , presents no marked zoological facies when contrasted with the upper, that of A. angulatus , which has a fauna exceeding in richness of species the remainder of the Lower Lias. The term “Infra-lias” has been given to this group of beds; but as its applicability varies with the classificatory views of individual authors, it seems, therefore, inadmissible; and, in my opinion, that of “Hettangian,” as suggested by Prof. Renevier†, should be used instead. The classification of the members of the Lias would then stand thus:— In England the Hettangian series contains a well-developed zone of Ammonites planorbis , whilst according to: Dr. Wright* “the zone of Ammonites angulatus , so far as it has been exposed, appears to be imperfectly developed in the British Isles; and from the difficulty experienced in separating its beds from the Bueklandi-series, they were grouped with the latter in my memoir.” This difficulty I have been enabled to overcome; and the determination of the zone of Ammonites angulatus with its characteristic fauna, in the localities hereafter to be mantioned, rests on lithological, stratigraphical, or palæontological evidence, or on a combination of two or all of these indices to the age of the horizon in question. II. O ccurrences of the Z one of A mmonites angulatus . 1. Ireland —The development of this zone in the neighbourhoods of

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