Scald the fish in boiling water, sufficiently to make the shells open; but do not let them be heated more than necessary. Clean them nicely, and then mix them with a white sauce. To give a pleasant flavour, add a little lemon-juice or vinegar.
Chop up a good quantity of garlic, onions, parsley, and red peppers (which last must be prepared by throwing them into boiling water, and rubbing off the skins with a dry cloth); scald the fish, and pick them out of their shells, then put all together in an olla (or round earthen pot), with plenty of oil; fry them till a deep yellow. They may either be served thus, or when finished add some broth, boil it up, and serve it like a thick soup.
The genuine Cadiz lovers of shellfish, however, consider that scalding the fish spoils it; they therefore prefer the raw fish being put at once into the oil and vegetables, and the dish is then sent to table with the shells in it. "Psammobia vespertina" has the following names in Spain, Navallinas and Guitzu-petit.