The generic diagnosis of Mehdiella Seurat, 1918 is emended based on study and redescription of Mehdiella microstoma (Drasche, 1884) from the caecum of Testudo graeca Linnaeus, 1758 collected in Settat, Morocco and on study and description of a new species, Mehdiella petterae sp. n., from the large intestine of Testudo hermanni (Gmelin, 1789) collected in Catalonia, Spain. Scanning electron microscopy (SEM) studies revealed substantial differences in the structure of the mouth and the caudal end, and made possible to differentiate the new species from the others. SEM studies showed the real and sound characteristics of the genus Mehdiella, namely number of anal papillae 2 instead of 3, post-anal papillae pedunculate or sessile instead sessile.