Montacutidae W.Clark 1855

(figures 99–102)

Material examined. A single shell with partially damaged rv from Stn 34, Gravier, south-east Rodrigues, 19 ‡ 43.9 ’ S, 63 ‡ 28.9 ’ E. NMW.Z.2000.086.00014.

Description. Shell 3.32 6 2.17 mm. Equivalve. Inequilateral, beaks close to the anterior margin. Outline elongate–subovate; anterior reduced, margin narrowly rounded; ventral and dorsal margins gently curved, oblique and subparallel; posterior broadly rounded. Small depressed lunule present. Sculpture smooth except for growth lines and faint radial striations which are most obvious under transmitted light. Hinge with prominent teeth in lv (figure 101), much weaker in rv (figure 102); small anterior tooth (at) at anterior end of lunule margin; remote posterior lateral tooth (pt) separated from beak by contiguous nymph. Internal resilium large, external ligament present on nymph. Inner margin smooth. Pallial line as a series of discontinuous scars. Shell white in colour.

Remarks. This shell is distinctive and unusual for the Montacutidae in its strongly inequilateral outline. We have placed this shell in the Montacutidae because of the lack of true cardinal teeth and the presence of a large internal resilium. In outline it is similar to Thecodonta A. Adams, 1864, but the dentitions, as given in Chavan (1969), do not agree.