The zonation of the Lias (Lower Jurassic) of the Northwest European ammonite province has been worked out in great detail and is based on very careful collecting from representative sections. It recently has been summarized thoroughly by Dean, Donavon, and Howarth (1961). In contrast, the zonation of the Pliensbachian Stage in the Alpine-Mediterranean province still is inadequate, despite extensive descriptive literature. There are several reasons for this.

1. Authors of ammonite monographs usually do not take into account the distinctive character of this faunal province, which requires zonation of its own, based on indigenous index forms. Efforts to correlate these assemblages with the classic zones established in Germany and England have led mostly to confusion.

2. During the Early Jurassic, most of the Alpine-Mediterranean province was undergoing a rapid and complex change of paleogeographic pattern, reflected in extreme heteropic differentiation. This process,

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highly irregular in time and space, commonly was accompanied by penecontemporaneous tectonic disturbances and hence anomalies in sedimentation, such as reworking, condensation, and gravity sliding. These complicating and potentially distorting factors usually have not been considered by those few authors who based their descriptions on material newly collected from measured sections rather than on material already existing in some museum collections. As a result, knowledge of the true vertical range of persistent and characteristic species, which would lead to the recognition of suitable index forms, is lacking.

3. Partly because of the two reasons just stated, the taxonomy of ammonite genera and species of this province is in need of revision. Many misidentifications and erroneous generic interpretations have to be corrected, particularly in the families Dactilyoceratidae and Hildoceratidae, both characteristic of the Mediterranean province.

Encouraging contributions to a clarification of the situation have come recently from studies of sections in Morocco, Portugal, and southwestern France. As a result of these studies, the two faunal provinces do not appear to be as distinctive as was previously assumed. In some of these sections, the provinces overlap, particularly in the Domerian Substage, thus making it possible to correlate a Mediterranean zonation based on hildoceratids with the established northwest European zonation based on amaltheids.

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