. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) The type specimen has been examined by us. Distribution. Found predominantly in tropical and subtropical latitudes, and southern temperate latitudes in the eastern Atlantic, at mid-slope to abyssal depths ranging from 943m to 4632m. Many protobranch species with robust shells having subrostrate or ovate outlines and with concentric ridges and external liga- ments, in the past have been referred to the genera Malletia, Neilonella orTindaria ( Dall, 1890). Ledella acinula is a case in point. Having addressed
. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) The type specimen has been examined by us. Distribution. Found predominantly in tropical and subtropical latitudes, and southern temperate latitudes in the eastern Atlantic, at mid-slope to abyssal depths ranging from 943m to 4632m. Many protobranch species with robust shells having subrostrate or ovate outlines and with concentric ridges and external liga- ments, in the past have been referred to the genera Malletia, Neilonella orTindaria ( Dall, 1890). Ledella acinula is a case in point. Having addressed this problem in earlier papers (Sand- ers and Allen, 1977, 1985), and the present, we have been able to define more rigorously the families Tindariidae. Neilonellidae and Malletiidae. Dall (1890) who described large specimens of L. acinula referred them to the subgenus Tindaria. Large specimens do show some resemblance to neilonellids and tindariids, but had Dall seen the shells of smaller specimens (Fig. 18), he would have been unlikely to have made the error. In our studies on Tindaria (Sanders and Allen, 1977) we re- examined and briefly redescribed L. acinula, and recognized that there was a problem in identification but deferred final judgment until we had made further comparative studies. Now that the Ledellinae have been reported upon (Allen and Hannah, 1989), the taxonomic relationship of this species is clear. ThatL. acinula is siphonate clearly distinguishes it from members of the family Tindariidae. Although similar to the neilonellids in having an external amphidetic ligament, it differs in having a small but well-defined internal ligament and in being semi-rostiate with a slightly sinuous postero-ventral margin. A further significant differ- ence is the form of the hind gut and the course that it takes within the body (Sanders and Allen, 1977). In L. acinula the hind gut is not particularly wide in diameter and is not restricted to the right side of the body (see b
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