This title was published by Smithsonian Institution Scholarly Press on 20 October 2009: Mead, J. G., and R. E. Fordyce. 2009. The therian skull: a lexicon with emphasis on the odontocetes. Smithsonian Contributions to Zoology 627:1-248. Abstract: Cetaceans form one of the most unique groups in the evolutionary history of mammals. They have returned to the sea and modified their tail as an efficient means of locomotion. As they adapted to the limited visibility in the aquatic environment, the odontocetes developed a system of echolocation that resulted in extensive modifications to the skull bones. This made descriptive comparisons very difficult and early anatomists unwittingly composed new terms for anatomical structures that had already been named in other taxa. This made anatomical comparisons, based on the literature, extremely tenuous. This lexicon is an attempt to remedy that situation in that it provides headwords and definitions for all the terms that have been used in describing the mammal skull and notes the synonymous terms. The lexicon includes the human nomenclature (Nomina Anatomica), the veterinary nomenclature (Nomina Anatomica Veterinaria) and the nomenclature that is used in descriptive comparative anatomy. The lexicon covers not only extant but extinct mammalian groups and is extensively indexed. The monograph is available as a free pdf download from the SI Press website via: www.sil.si.edu/smithsoniancontributions/Zoology/ The authors realise there is no end to lexicography, and are already compiling terms for a second edition in which we plan to include mysticetes. With this aim, we would welcome comments on entries in the current volume. It will help if your email subject line mentions "Lexicon". James G. Mead, Ph.D. Curator of Marine Mammals Division of Mammals, Smithsonian Institution NHB 394, MRC 108 P.O. Box 37012 Washington, DC 20013-7012 R. Ewan Fordyce Head, Department of Geology, University of Otago, PO Box 56, Dunedin 9054, NZ, and Research Associate, Division of Mammals, Smithsonian Institution