During the Early Ordovician, much of the Laurentian paleocontinent was flooded by shallow, warm seas in which a great variety of endemic trilobites evolved, particularly those belonging to the family Bathyuridae. These have been collected and well studied from many localities across the Great Basin and adjacent areas. Deeper-water trilobites belonging to biofacies in peripheral sites around the carbonate-rich platform have a much poorer fossil record, largely because later tectonics have erased the appropriate sites. We describe here a rare example of a relatively low-diversity trilobite fauna of this kind recovered from the Al Rose Formation in the Inyo Mountains, California. Trilobites of the families Metagnostidae, Olenidae, and Raphiophoridae are well represented in this fauna, although they are rare or unknown from contemporary platform carbonates.

The Lower Ordovician (Floian) Al Rose Formation from the Inyo Mountains, California, is a deeper-water, graptolitic equivalent of the well-known and richly fossiliferous successions described from Utah and Nevada. It is considered to have been originally marginal to the Laurentian paleocontinent. It has yielded a low-diversity trilobite fauna that differs strikingly from contemporary faunas to the east in its abundance of raphiophorid, nileid, olenid, and agnostoid trilobites, resembling that of the Nileid Biofacies known from scattered locations marginal to Laurentia. Two new trilobite species are described: Globampyx sexsegmentatus (Raphiophoridae) and Protopresbynileus divergens (Nileidae). Carolinites genacinaca Ross, 1951 is a link with the Great Basin. Other trilobites include the olenid Cloacaspis cf. C. ceryx anataphra Fortey, 1974, metagnostid Geragnostus cf. G. (Novoagnostus) longicollis Raymond, 1925, and pliomerid Hintzeia sp.