Dear Recorder,
The shell of Patella vulgata is very often as low as on P. depressa, and is very frequently mistaken for it in Britain and Ireland. If yours is a dead, fresh shell, please remove loose debris and position it carefully to take 3 views, as above. A single exterior view is very unlikely to be sufficient for verification.
Records for P. depressa can only be verified on iRecord with an image that shows some or all of these features:
1) dark brown/black foot (insufficient alone as P. vulgata sometimes as dark).
2) chalky white, opaque pallial tentacles around periphery (best seen when attached to glass in water, as on left, above).
3) chalky white marks near tips of ribs on interior (may be lost by erosion).
4) apex of shell offset towards anterior (insufficient alone as applies also to P. ulyssiponensis).
5) interior colouring (often helpful, but not always because of wide variation).

Records claimed anywhere in Ireland, or out of area in Britain and northern Europe, as demonstrated by the map and caption at 40 Patella depressa. Distribution in Britain. , require 1 & 2 for acceptance, as such records would change the understanding of this species. For full details please read the account at flic.kr/s/aHskokisge .

If using historic publications or transferring historic records be aware that ‘Patella depressa’ was used for what is now accepted as Patella ulyssiponensis . See synonyms section at 01 Patella depressa. Length 32mm, height 9.1mm. S. Devon. September 1997. Leg. J. Light. .

Because P. depressa is apparently one of the commonest limpet species in southern Europe there seems to be a tendency on iNaturalist for records of any limpet there to be identified by some recorders as it by default.
P. ullyssiponensis, P. vulgata and P. rustica are all widespread in Galicia. Southwards, they are joined by other limpet-form species, such as Siphonaria pectinata. Many of these may be mistaken for P. depressa when only a single exterior image is shown. In such cases, the generalised suggestion of ‘Patellogastropoda’ should be used (though S. pectinata is not in that subclass).
For Atlantic coasts of Iberia, a useful aid is Trigo et al. 2018. Guia de los Moluscos Marinos de Galicia.

The morphological features of P. ulyssiponensis, P. depressa, P. vulgata and (in Spain) P. rustica show “high morphological plasticity and are influenced by environmental conditions, leading to an overlap of states between different species”. Allozyme studies showed “high differentiation and no evidence of hybridisation” of the species (Sá-Pinto et al. 2007 www.vliz.be/imisdocs/publications/131981. pdf ). Individuals with intermediate morphological characteristics result from the accentuated morphological plasticity of these species, not hybridisation. Without molecular examination, they often cannot be confidently assigned to a particular species and should not be recorded as such.