What is the Flamenco Seguiriyas?
Flamenco Seguiriyas, also spelled siguiriyas, siguerillas, or siguirillas, is a deep, expressive style evoking a tragic feeling similar to the Soleá. Slow, somber, and sentimental, the Siguiriyas compás follows the 12 beat cycle but with a different accent pattern than the Soleares as seen here:

In standard notation, the Seguiriya is commonly represented with alternating bars of 3/4 and 6/8 time, allowing the player to strongly feel the 5-count as described above.
Flamenco Seguiriyas Examples and Links
Here are some of my favorite exemplary Seguiriyas: