Summary. An attempt has been made to present a full account of the anatomy of the head (exclusive of the inner ear) of Leiopelma. Material from two species, Leiopelma archeyi and Leiopelma hochstetteri, has been studied and the head of the latter is here described for the first time. As far as possible, comparison has been made with the head of Ascaphus, the only other genus included in the same primitive anuran family. Specific differences between Leiopelma archeyi and Leiopelma hochstetteri are described and listed. A possible homology is suggested between the processus lingularis of Anura and Seydel's palatal process of Urodela. Particular emphasis is placed on the controversial topic of the basal connection between the quadrate and the neurocranium. An historical account of previous ideas on this subject is included, followed by a discussion based on the view that the ‘basal’ or ‘pseudobasal’ process of Leiopelma, together with the ledge of cartilage forming the floor of the hyomandibular canal, are of hyoid origin.

The chromosome complements of four specimens of the anatomically primitive frog Leiopelma hochstetteri are described from cultured cells and squashes. The basic karyotype in all cases consists of 22 chromosomes, 12 of which are acrocentric. Supernumerary chromosomes are either absent or variable in number, but appear to be constant in the somatic cells of any one individual. The limited evidence available suggests that the supernumerary chromosomes do not pair during male meiosis.The karotype of L. archeyi is described for the first time. Only the smallest pair of the total complement of 18 chromosomes is acrocentric. Supernumeraries are absent.The distribution and probable relationships of the species of Leiopelma are discussed. The karyotypes of Leiopelma and the North American ascaphid frog Ascaphus truei are compared, with particular reference to the relationship of the supernumerary chromosomes of Leiopelma and the microchromosomes of Ascaphus.

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