הזיהויים של gulvain

We must show some inside detail if we want our marine shells identified. The outside shapes, colours and textures are often lovely but will not always lead to a definitive ID.
Venerupis corrugata The Pullet has the perfect shell for internal features. It is rare to find one where the internal architecture is not on view - picture 2. One might have to turn it in the light a little to show the lines.
Like all shells it is probably best to take it to a base and examine it under good lighting but it is not difficult to ID in the field by shape alone - pictures 3 & 4.
Compared to other common shells it is often easy
It has an interesting and uniform angle which can be seen and measured - picture 5.
I have found some cell phone apps are quite useful for some things - more in another Observation.
But no special skills or apps are required for the Pullet. It even looks like a squat hen at times - pictures 6 & 7.
It often has a blue tinge to the inside wings - picture 8. Actually it's a rather nice shell!

See http://www.fao.org/fishery/culturedspecies/Venerupis_pullastra/en

One should read ALL the added comments below.
It is true that there might be doubt about one of the examples shown.
The reason for leaving the Photo and text, as in the original, is so that others can associate Comments with photos. I am very loath to break that useful and valuable association

Possibly the most telling quick ID feature is shown in picture 3, they fit to form a near circle.
But, as always, we need to rely on the inside architecture for a acceptable ID, thought it is sometimes difficult to photograph the features and NOT always conclusive.
It is worth looking closely at the upper and lower surfaces of hinge left-valve laterals and inner surfaces of right-valve lateral - they are serrated, worth seeking out, satisfying to observe. Pictures 9 & 10.
This is a broadly triangular, very robust and common shell. It can be confused with Spisula subtruncata

Razor-shells need careful consideration when attempting identification. The key areas are highlighted in Picture 1
The Pallial Line is the most useful field-feature and one should angle the specimen, so that the light may reflect from these lines. They are not always easy to see nor photograph..
The Hinge Teeth are usually visible but require more detailed knowledge or a text key to hand,
The Atlantic Jackknife
Ensis leei (see Comments) has a unique Pallial Sinus and teeth arrangement. It is commonly found in Europe and can be mistaken for Ensis ensis https://www.gbif.org/species/8485639