Sphenodiscus binckhorsti Boehm 1898 in het Krijt van Zuid-Limburg

The occurrence of the ammonite Sphenodiscus binckhorsti BOEHM 1898 in the Upper-Cretaceous of Southern Limburg, the Netherlands, has been mentioned for the first time by Binkhorst van den Binkhorst (1859a) who gave a detailed description of his material, using the name Ammonites pedernalis VON BUCH 1849. Although aware of differences between his material and Von Buchs descriptions he considered these of minor importance. Meek (1876) suggested a similatity between the specimens described by Binkhorst and Sphenodiscus lenticularis OWEN 1852. According to De Grossouvre (1893) the Limburg specimens had to be assigned to Sphenodiscus ubaghsi DE GROSSOUVRE 1893. Boehm (1898) reviewing Ammonites pedernalis VON BUCH 1849, considered the Limburg specimens as belonging to a seperate speciec and introduced the name Sphenodiscus hinckhorsti. When studying the literature the impression is obtained that most authors had-only very few material at their disposal. The systematical position of the Limburg specimens can only be determined by an elaborate study of the original material, described by these authors. A suchlike critical revision however is not possible since an important part of the original material has been lost. Instead of this exact description is given of all specimens found in the Limburg area, in order to obtain a basis for further investigation. 48 partly fragmentary specimens have been studied, mainly originating from the highest part of the Maastricht Chalks (Zone M of Hofker 1966 and Md of Uhlenbroek 1912). Binkhorst sections are compared with the well known section in the quarry „Curfs" at Geulhem. Based on this comparison it is highly probable that Binkhorst' material (still present in the Palaeontologisches Institut of the Humboldt University in Berlin) was found in the same stratigraphical zone as the recently collected specimens. Owing to the relatively small horizontal extension of this zone in the area around the village of Valkenburg both the most probable location and stratigraphical position of Valkenburg both the most probable location and stratigraphical position of the holotype could be indicated.