The José Formation represents a unique medium-gray, quartz sandy, bioturbated, oolitic limestone within the El Paso Group of southern New Mexico and westernmost Texas. Although the José is commonly cited as being abundantly fossiliferous, only Flower (1968) has provided documentation of this low diversity trilobite fauna.

The most common species from the José was named by Flower (1968) as Aulacoparia ? huygenae. Recovery of hypostomes associated with topotype material from Cooks Peak, New Mexico, confirms Flower’s assignment to genus. Additionally, we extend the geographic range of A. huygenae to include occurrences in the Florida and Caballos Mountains. Uncommon among collections from Cooks Peak and the Big Hatchet Mountains are 2 undescribed species that may be assigned to Jeffersonia. The first species is finely granulose with a short (sag.), rectangular glabella and which bears a short occipital spine and node on the anterior 2 axial rings. The second species is smooth with an elongate (sag.), keeled glabella, exhibits a longitudinal furrow bisecting the preglabellar field, and may include the Oculomagnus sp. illustrated in Flower (1968). Interestingly, these Jeffersonia species replace A. huygenae as the dominant taxa in collections from the Caballos Mountains. Rare specimens of Leiostegium complete the fauna.

Aulacoparia huygenae and both species of Jeffersonia are, to date, restricted to the José. This suggests that their distribution may be ecologically controlled by the deepening event that governed the onset and cessation of oolite deposition.