ABSTRACT. – Patella ferruginea (Gmelin, 1791) is a prosobranch gastropod endemic to the western Mediterranean and considered as an endangered species. This limpet has two ecotypes and morphologies [Rouxii (conical non-centric) and Lamarckii (depressed and concentric)]. Geometric morphometric techniques allow the analysis of variation in biological shape and have not been used before to study the morphological dissimilarities between the Rouxii and Lamarckii forms. Individuals of these two forms were collected from seven stations of the Algerian coast. Biometrical characters [the total length (L), the total width (W), height (H), the distance between the apex and the anterior edge of the shell (DA) and the distance between the apex and the posterior edge of the shell (DP)] were measured on each specimen. In order to analyze morphological dissimilarities between the Rouxii form and the Lamarckii form, a discriminative analysis was performed using morphometric variables [the ratios (H/L, H/W, L/W, DA/DP) and the geometrical mean (GM)] supported by an outline shape analysis of the shells. The results showed that Rouxii form is high and voluminous with an outline tending towards a circular shape; whereas, Lamarckii form is flattened and concentric with an outline tending towards an elliptic shape. The vertical migration and the environmental pressures could be the reasons explaining the dissimilarity between Rouxii and Lamarckii forms.