In the Trimerellidae, for example, some of the muscles are attached to a massive or vaulted platform situated in the medio-longitudinal region of the posterior half or umbonal portion of both valves. [Please select]
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Right-hand scutum alone furnished with an internal umbonal tooth: uppermost part of peduncle dark-coloured. [Please select]
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_ Valves smooth, thin, brittle; scuta with internal umbonal teeth on both sides. [Please select]
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_ Valves approximate, slightly furrowed, especially the terga; right-hand scutum with a strong internal umbonal tooth; left-hand with a small tooth, or mere ridge; occludent margin arched, protuberant: uppermost part of peduncle orange-coloured. [Please select]
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_ Valves 5; carina with a truncated and crested base; scuta with strong internal umbonal teeth; terga with the basal point truncated, almost parallel to the occludent margin. [Please select]
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