. Bulletin of the British Museum (Natural History), Geology. ventral body musculature {Acipenser, Jessen 1972 : pi. 13, fig. 1) and did not attach to the pectoral girdle. In teleosts the clavicles are lost; the sternohyoideus muscle originates on the outer surface of the elongated ventral arm of the cleithrum {Elops, Jessen 1972 : pi. 7, fig. 4) or again is con- tinuous with the ventral body musculature {Salmo, Jessen 1972 : pi. 15, fig. 1). In Lepisosteus and Amia the sternohyoideus muscle has a similar area of origin to that oi Elops. Two or three elongated plates of bone, bearing scattered
. Bulletin of the British Museum (Natural History), Geology. ventral body musculature {Acipenser, Jessen 1972 : pi. 13, fig. 1) and did not attach to the pectoral girdle. In teleosts the clavicles are lost; the sternohyoideus muscle originates on the outer surface of the elongated ventral arm of the cleithrum {Elops, Jessen 1972 : pi. 7, fig. 4) or again is con- tinuous with the ventral body musculature {Salmo, Jessen 1972 : pi. 15, fig. 1). In Lepisosteus and Amia the sternohyoideus muscle has a similar area of origin to that oi Elops. Two or three elongated plates of bone, bearing scattered denticles and patches of ganoine, are embedded in the skin covering this muscle in Lepisosteus (Liem & Woods 1973 : pi. 4b); Jarvik (1944) considered these plates homologous with the clavicles of chondrosteans. Since both lie lateral to the sternohyoideus muscles, this seems likely. If the identification is correct, there is no doubt that the serrated plates and appendages of Amia, Caturus and Propterus are derived from the clavicle too. However, in Lepisosteus, additional bony plates may occur on the cleithrum (Fig. 51). They are much smaller than the two or three large plates described by Jarvik, which they resemble in bearing denticles and ganoine. The smaller plates lie alongside the larger plates, and in the skin covering the dorsal arm of the cleithrum. Thus bony plates are able to form in the dermis over a large area of the cleithrum and it is by no means clear that this ability is derived from the ability to form the clavicle of chondrosteans. Whatever the homologies of the serrated appendage in Propterus, its presence cannot be taken as evidence of relationship with the amiid-caturid group until the distribution and form of this element is more widely known among the Neopterygii. Although suggestions have been made (Wilder 1876 : 259, Wright 1884, Liem & Woods 1973), the functions of the serrated appendage remain a mystery. (ix) Dorsal and anal fins. The macros
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