Published online by Cambridge University Press: 19 May 2016
Propeamussium (Parvamussium) holzense n. sp. and Propeamussium (Parvamussium) robinsonense n. sp. are described from the Upper Cretaceous Holz Shale Member of the Ladd Formation, Santa Ana Mountains, southern California. These species occur with Bostrychoceras elongatum (Whiteaves), Glyptoxoceras subcompressum (Forbes), and Inoceramus orientalus (Sokolow), which are indicative of a late medial Santonian age (Bostrychoceras elongatum Biochron). Propeamussium (Parvamussium) cowperi (Waring), from the Campanian Chatsworth Formation of the Simi Hills, southern California, is also redescribed and reillustrated for comparative purposes.