. Bulletin. Natural history. THE MANDIBLE OF DIPNORHYNCHUS SUSSMILCHI EXTERNAL DERMAL BONES The external surface (Figs. 18 and 19) is composed of four infradentary bones on each side and a dentary in front. These are well preserved on specimen P 46773 except on the posteromedial surface. The upper surface of the right side of speci- men P 33714 also shows fine detail, but on the Buchan specimen (P 13837) the outer dermal bones are much more fragmentary. Nevertheless, the same number and arrangement of bones can be detected. Perhaps the simplest approach to these bones is through a direct compa
. Bulletin. Natural history. THE MANDIBLE OF DIPNORHYNCHUS SUSSMILCHI EXTERNAL DERMAL BONES The external surface (Figs. 18 and 19) is composed of four infradentary bones on each side and a dentary in front. These are well preserved on specimen P 46773 except on the posteromedial surface. The upper surface of the right side of speci- men P 33714 also shows fine detail, but on the Buchan specimen (P 13837) the outer dermal bones are much more fragmentary. Nevertheless, the same number and arrangement of bones can be detected. Perhaps the simplest approach to these bones is through a direct comparison with Dipterus platycgphalus for which Watson and Day (1916) have provided a nomenclature that is widely applied in its original, or a slightly modified, form (Goodrich, 1930; Westoll, 1949; Lehman, 1966; Denison, 1968a). As will be seen below, there are good reasons for believing that the homologies indicated by this nomenclature are correct. The dentary poses no difficulties. It is a relatively long structure compared with that of other Devonian genera, and on the ventral surface is slightly longer medially than laterally. There is no sign of a median symphysis. Its outer anterior surface is well rounded in general, but it carries a shallow groove that arises posterolaterally from the labial pit (Jarvik, 1964) and runs back along its poste- rior margin. The upper edge of the dentary extends back along the ramus of the jaw for approximately two-fifths of its total length. Just inside its upper edge there is a pr art h sal. psp Fig. 18. Dipnorhynchus sussmilchi, lower jaw in left lateral view. Based on specimens P 46773 and P 33715, British Museum (Natural History). 44. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody Museum of Natural History. New Haven, Peabody Museum of Natural History, Yale U
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