AS WITH "USA Clay," a single-medium survey of the ceramicist's art that the Renwick Gallery put together three years ago, the homeliest pieces are the best in the Cultural Institute of Mexico's "The Dream of Earth: 21st-Century Tendencies in Mexican Sculpture." There's something about the baseness of clay here that convinces you of this: the uglier the better.

Read through the show's catalogue, wall text and the accompanying artists' statements, and a certain theme begins to emerge from the manner in which these six artists and their work are written about. Adjectives like "essential," "organic," "primitive" and "elemental" appear, along with such concepts as "honesty" and "leaving behind all sophistication." This is not a show of the potter's pretty craft, of delicate, eggplant-colored raku vessels and stoneware party platters painted in a bamboo motif. The strongest works here resemble simple cacti or, better still, to use filmmaker John Waters's description of a particular Cy Twombly sculpture, "a most confident and graceful depiction of Godzilla's discharge."

That's right. One of the most strikingly "elemental" artworks in the whole show looks like nothing so much as a towering pile of excrement. It's one of the first works you'll see, and it comes courtesy of sculptor Gerardo Azcunaga, whose works also evoke fear and recognition through the imitation of strange organs, toothed pods and other hybrid body parts.

Of course, there's nothing particularly new about bodily associations with clay. Even traditional ceramic vessels acknowledge this in the nomenclature used in discussion of their various parts: the lip, the foot, the mouth, the arm. It is in the ways that "The Dream of Earth" departs from tradition, however, that make it special.

That's why such artists as Javier Marin and Maribel Portela -- whose works cleave closely to academic, or in Portela's case, pre-Columbian, figuration -- stand out, and not in a good way. They're overly familiar in their evocation of the human form.

Although Miriam Medrez makes ample use of the human body, too, she at least dresses it up with "suits" made of pipe cleaners, "skins" of rice paper printed with the photographic image of cracked soil and patinas of crushed black stone. Medrez's bold experiments with surface -- she also uses wax and, in the case of her surreal cactus plants, wire mesh -- are fruitful beyond what you'd expect.

Artist Paloma Torres (who also curated the show of this loosely knit group, all of whom have exhibited together elsewhere), expresses herself with what might be called a self-limiting vocabulary: the tower. Yet her miniature urban landscapes, all of which incorporate some permutation of architecture, are not muted by their formal sameness. They sing, with a clear and darkly poetic voice, a song about the life, death and rhythm of cities.

Adriana Margain's work seems least in keeping with the overall rough-hewn aesthetic of this show. Even keeping in mind the fact that this is a small survey organized around the more loosey-goosey term, "tendencies," not even "trends," her sculptural forms come across as too finished, too polished, too much like, well, pottery than like the earth from which they came.

It's when the art of "Dream" -- exemplified by Azcunaga's raw, rudely beautiful and down 'n' dirty forms -- remembers where it, and we, came from, and will one day return, that it is most powerful. "We were clay," after all, notes Portela, referencing the Popul Vuh, an ancient Mayan scripture. At its best, "The Dream of Earth" reminds us that we still are.

THE DREAM OF EARTH: 21ST-CENTURY TENDENCIES IN MEXICAN SCULPTURE -- Through Nov. 11 at the Cultural Institute of Mexico, 2829 16th St. NW (Metro: Columbia Heights). 202-728-1628. Open Monday-Friday 10 to 5:30. Free.

Gerardo Azcunaga's "Fountain" at the Cultural Institute of Mexico evokes fear and recognition.Miriam Medrez's untitled sculpture is part of "The Dream of Earth" exhibit of "elemental" clay works.