Paleoecology of the lowermost Carmel Formation, San Rafael Swell, Emery County, Utah, was studied at nine localmes 2 to 21 miles apart. Eight of the sections contain fossiliferous calcilutites and oolmc limestones in the basal 35 to 135 feet measured. Thickness of the fossiliferous beds ranges up to 10 feet. Beds of barren calcilutites, calcarenites, oolmc limestones, intraclastic limestones, calcareous sandstones, and bedded gypsum, separate the fossiliferous beds. A parallel-bedded, basal quartz sandstone, 0.5 to 7 feet thick, everywhere overlies the Navajo Formation. Molluscs dominate faunal assemblages. Shells are recrystallised to calcite, but external sculpture is preserved in sufficient detail for identification. Lamellibranchs are represented by disarticulated shells in unbroken condmon, oriented convex up. Fossil assemblages constitute four main types: (1) Two widespread and heterogeneous assemblages dominated by Camptonectes sp.; (2) A restricted assemblage consisting only of Trigonia Spa in the northern Swell; and (3) A restricted assemblage consisting only of Ophiomorpha burrows in the southern Swell. Associated with Camptonectes Spa are the lamellibranchs Vaugonia sp., Pronoella sp., Trigonia sp., Lima sp., (?)Ostraes sp., (?)Gryphaea sp., and Isognomon sp.; the gastropods Cossmanea Spa and Nerinea sp., and the crinoid Pentacrinus sp .. Fossil assemblages show an imbalance; Herbivores and sediment feeders are absent, and carnivores (predators) and scavengers (selective detritus feeders) are rare. Disarticulation without great breakage suggests gradual deposmon of shells and carbonate material under moderate energy condmons. On the basis of closest living relatives, the assemblages found in carbonate rocks indicate a wide tolerance of these animals to fluctuations in salinity and temperature. The well developed byssal notch of some pectinids suggests abundant vascular plant live. Abundantly fossiliferous beds are separated by barren beds with some evaporites, a sequence suggesting a warm sea of varying but high salinity. Grain-size ranges and limestone predominance indicate, respectively, differing lateral energy levels, and a low terrigeneous clastic influx.