Several authors have pointed out that the genus name Lopha Roding, 1798 included a rather heterogeneous stock, but had traditionally maintained that name in a wide sense because they regarded that these forms represented an evolutionary line (see for instance Stenzel, 1971; Siewertr„1972). On the other hand Malchus (1990, p. 187) considered that Triassic and Jurassic species previously referred to Lopha do not have any phylogenetic relationship with the living Lophinae. Consequently, he erected the new family Palaeolophidae to accommodate them and the new name I'alaeolopha, mainly based on details of shell structure. Although the genus is not weH characterized on morphological grounds and there is no possibility to study the shell structure of the Mexican speci- mens, it is adopted here because it is the best available generic name for the species O. haidingeriana, which cannot be referred to either I.op&a or ActinostreoII. Bayle, 1878.

Pnlueolophn cf. I'. haidingeriuIta (Kmmrieh, 1853)
(Figure 8.5 — 8.7)

Cf. 1853. Ostrea haI,dingeriana Emmrich, p. 377.

Cf. 1860. "Ostrea" marcIgvyana Martin, p. 90; p1. 90, figs.

24-25.

Cf. 1908. A/ectrvonia cf. haidingeriana Elm.; Healey, p. 37,

pl. 5, figs. 17 — 19.

Cf. 1971. I.omaha haidingeriana (Emmrich); Stenzel, fig. J62.4.

Material — Four almost complete shel ls and several she11 frag- ments, preserved as internal or external moulds (ERNO-814 to 816, 1954 to 1956) from the Antimonio Formation, unit 12; Upper Triassic (Norian7); Sierra del Alamo, sections 1 and 2.