. Bulletin of the British Museum (Natural History), Geology. PALAEOZOIC ANOMALODESMATA Family EDMONDIIDAE King, 1850 Genera referred here to this family are Edmondia, Allorisma, Scaldia and Cardiomorpha, which all possess a hinge plate reinforced internally by a ridge or lamellar plate projecting into the shell cavity; it is equivalent to the 'internal cartilage plate or ossicle' (Wilson 1960, Waterhouse 1969a, Runnegar & Newell 1974). Earlier, one of us (Dickins 1963) had suggested that the Megadesmidae might be included in the family Edmondiidae, but this relationship has been discussed
. Bulletin of the British Museum (Natural History), Geology. PALAEOZOIC ANOMALODESMATA Family EDMONDIIDAE King, 1850 Genera referred here to this family are Edmondia, Allorisma, Scaldia and Cardiomorpha, which all possess a hinge plate reinforced internally by a ridge or lamellar plate projecting into the shell cavity; it is equivalent to the 'internal cartilage plate or ossicle' (Wilson 1960, Waterhouse 1969a, Runnegar & Newell 1974). Earlier, one of us (Dickins 1963) had suggested that the Megadesmidae might be included in the family Edmondiidae, but this relationship has been discussed by Runnegar & Newell (1974), who showed that Allorisma, Scaldia and Cardiomorpha also had an internal lamellar plate as well as having other characters in common with Edmondia. On the basis of this information and further data presented here we also conclude that the Edmondiidae and the Mega- desmidae should be recognized as separate families. Edmon- diids from western Europe such as Cardiomorpha obliqua Hind (1898: 263) and Edmondia lyellii Hind (1899: 300) are the most similar to typical Australasian genera Megadesmus, Pyramus and Astartila. We imagine the ancestry of the Megadesmidae to have been from taxa such as these. Cardio- morpha obliqua in particular is thick-shelled for an edmondiid. Although its hinge margin is quite thick, the internal rib is only just distinct and its adductor and accessory muscle scars are rather similar to those of the megadesmids. We suspect that the species of Vacunella, Australomya and Myonia from eastern Australia are true anomalodesmatids, which are not 57 necessarily closely related to the megadesmids. Periostracal spicules are not usually preserved on the shell surface of Edmondiacea, but Runnegar (1965: pi. 13, fig. 9) clearly illustrates their presence in Megadesmus gryphoides (de Koninck). We are unable to say whether they originally occurred on other taxa within this superfamily. We follow Astafieva-Urbaitis (1964) and Runnegar &a
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