. Bulletin of the Natural History Museum Zoology. 78 ALLEN, SANDERS AND F. HANNAH Jean Charcot DS37 2110 1 47°'N 8°'W DS (Biogas III) (Biogas IV) CP01 2245 2 47°'N 8°'W CP 25. CANARY BASIN Discovery 6704 2129 1 27°'N 14°'W ED This is predominantly a northern Atlantic species occurring mostly from 10-200 metres (Ockelmann, 1958). Neverthe- less, there are sufficient past records to confirm the present identifications that at its southern limits it is present at lower slope depths. Perhaps indicative of a temperature/depth relationship. Shel
. Bulletin of the Natural History Museum Zoology. 78 ALLEN, SANDERS AND F. HANNAH Jean Charcot DS37 2110 1 47°'N 8°'W DS (Biogas III) (Biogas IV) CP01 2245 2 47°'N 8°'W CP 25. CANARY BASIN Discovery 6704 2129 1 27°'N 14°'W ED This is predominantly a northern Atlantic species occurring mostly from 10-200 metres (Ockelmann, 1958). Neverthe- less, there are sufficient past records to confirm the present identifications that at its southern limits it is present at lower slope depths. Perhaps indicative of a temperature/depth relationship. Shell description (Fig. 126). Shell moderately stout, ovate, slightly inequilateral, fine concentric lines, with elon- gate lunule and escutcheon, shell very wide dorsally and medially (such that when it rests on a valve the dorsal part is centred so that both umbos are characteristically visible in the lateral view); umbo very large, raised, internally directed, orthogyrate, immediately anterior to midline; antero-dorsal margin joins anterior and antero-ventral margins in a smooth curve, postero-dorsal margin also joins posterior and postero- ventral margin in smooth curve but is more attenuate than anterior margin; hinge plate moderately stout, not quite reaching level with the outer margins of adductor muscles, hinge plate narrows almost to margin below umbo, anterior and posterior hinge teeth equal in number or with one additional on the posterior plate; ligament amphidetic large, globular, extending far ventral to the hinge plate, slight secondary anterior and posterior external extension of fused periostracum. (See Ockelmann 1958, for typical shell dimen- sions). Internal morphology (Fig. 127). The combined siphons are short within a relatively shallow siphonal embayment. There is a slender sensory tentacle on the right side. The anterior sense organ and the feeding aperture are not particu- larly well-developed. The adductor muscles are very large, more or less oval in
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