Ebert's review of Un chien andalou provides both a good analysis of the film to use as a comparison to The Seashell and the Clergyman and a good example of the main arguments put forth in support of Un chien andalou as the first Surrealist film.  According to Ebert, the idea for the film originated from a discussion between Dalí and Buñuel about dreams they had had, prompting them to make a film beginning with images from their dreams.  “In collaborating on the scenario, their method was to toss shocking images or events at one another. Both had to agree before a shot was included in the film. 'No idea or image that might lend itself to a rational explanation of any kind would be accepted,' Bunuel remembered. 'We had to open all doors to the irrational and keep only those images that surprised us, without trying to explain why'” (Ebert).  Ebert also asserts the historical primacy of the film: “It was made in the hope of administering a revolutionary shock to society. 'For the first time in the history of the cinema,' wrote the critic Ado Kyrou, 'a director tries not to please but rather to alienate nearly all potential spectators.'”
    Ebert's review provides much useful information for a comparison of Un chien andalou and The Seashell and the Clergyman and the theories behind them.  To begin with, the technique used by  Dalí and Buñuel in writing their film was quite different than those used by Dulac and those theorized by Artaud.  Ebert argues that Dalí and Buñuel sought to create a film entirely devoid of meaning with no rational connection between any of events or images, essentially a film of pure nonsense.  This varies considerably from Artaud's ideas of creating an experience that betrays a traditional narrative setting (requiring at least some connections between parts of the film) in order to include the spectator in the film.  The goal of  Dalí and Buñuel was to create a film that left the viewer with nothing and no ability to derive meaning from the experience; whereas, Artaud's goal was to force the audience to be a part of the dream world and create interpretations and conclusions on their own.  Additionally, the technique of throwing illogical, surprising images at the audience used by Dalí and Buñuel was a primary technique in Dulac's film as well.  Ebert and Kyrou advocate the uniqueness of Un chien andalou as film's first attempt to alienate an audience, but ignore the attempts of The Seashell and the Clergyman to alienate the audience from identification with the film and many other previous films such as The Cabinet of Dr. Caligari and Impressionist films.  While differences between Un chien andalou and The Seashell and the Clergyman may be noted from their difference in purpose, the theory and techniques used in both originated with Dulac's film.

Ebert, Roger. "Un chien andalou (1928)." Rev. of Chicago Sun-Times. Chicago Sun-Times 16 Apr. 2000.