Cambrian (Guzhangian) trilobites from the Weeks Formation of western Utah, USA

The Weeks Formation (Cambrian System, 500 Mya) of western Utah has long been renowned for its exceptional preservation of soft-bodied marine organisms and articulated trilobites. Due to the abundance of fully articulated exoskeletons, the trilobite fauna is a rare and important source of morphological information. However, the fauna has seen limited scientific study, with only a handful of published works over the past century, and the most common species described by Walcott in 1916 have never been photographically reillustrated. Here, new descriptions and illustrations of some of the more commonly occurring and widely cited trilobite species from the Weeks Formation are provided based on newly collected material. Descriptions for the species Menomonia semele (Walcott, 1916), Cedaria minor (Walcott, 1916), Weeksina unispina (Walcott, 1916), Genevievella granulata (Walcott, 1916); and discussion of Dresbachia sahratiani (Robison and Babcock, 2011), Modocia whiteleyi Robison & Babcock, 2011, and Tricrepicephalus Kobayashi, 1935 permit for more detailed assessments of their relationships to other species.