Five new mollusks are described from shallow-marine deposits of the lower middle Eocene Llajas Formation, northeastern Simi Valley, Southern California. Most of the mollusks are confined to a 1-m-thick bed informally known as the "Stewart bed" and are part of an Eocernina-Turritella-Crassatella community. Cymatium (Septa) janetae n. sp. is at present the earliest species worldwide referable to Septa. Ranella katherineae n. sp. is one of the earliest West Coast species of Ranella s.s. A new species of Clavilithes occurs with C. tabulatus (Dickerson); C. tabulatus was previously regarded as being of early Eocene age only. Pinna llajasensis n. sp. is conspecific with Pinna n. sp. Vokes from the middle Eocene Domengine Formation of central California. A partial phragmocone of a spirulimorph sepiid, family indeterminate, is the first record of a sepiid in the Eocene of western North America.--Journal abstract.