Soon after commencing a taxonomic study of larvae of the Oedemeridae, I discovered that there was no single publication which could be consulted in order to gain an understanding of their anatomy. Consequently I undertook a study of the exoskeleton of the mature larvae of Nacerdes melanura (Linnaeus), a common representative of the family. The investigation revealed that the morphological terms that had been applied to beetle larvae were not always consistent with modern practices. More important, however, was the fact that the homologies of some of the structures had been misinterpreted or were unknown. This paper, therefore, is intended to serve two purposes: to establish the homologies of the external structures of the mature larva of Nacerdes melanura and to provide a terminology that conforms with present-day usage in insect morphology. I believe, however, that the material may have a broader application. An examination of representatives of a number of coleopterous families reveals that the morphological terms and the concepts of the structures presented here can be applied to most legged orthosomatic beetle larvae. Furthermore, since it seems likely that this type of larva gave rise to the various grub-shaped and apodous forms, the investigation would seem to be a necessary step in interpreting homologies throughout the order.