Lyrodesma inornatum

• Shell not known to exceed 18 mm. in length, transversely subovate, compressed convex, the three dimensions length, height and thickness respectively to each other as nine and seven is to four. Anterior margin regularly curved, base broadly convex, posterior margin slightly oblique, strongly rounded and most prominent below, gently curved and sloping forward above to the subangular extremity of the short hinge line. Beaks rather small, moderately prominent, situated a little in front of the center; cardinal slope compressed, slightly alate; umbonal ridge very moderately developed, the greater part of the surface being rather evenly convex. Surface nearly smooth, without radial lines on the cardinal slope, in the best specimens exhibiting only a small number of obscure concentric lines of growth. Eight transversely striated and radially arranged cardinal teeth in each valve, the anterior one usually not quite distinct from the dorsal edge of the valves. Muscular and pallial impressions not observed.
• This species agrees with L. planum Conrad, in the number of its cardinal teeth and in wanting the post-cardinal striae which are usually present in species of the genus. They are however readily separated by differences in their outlines, L. inornatum being shorter (relatively higher) and more nearly ovate. Hall’s L. cincinnatiense presents considerable resemblance in the way of outline, yet is really quite a distinct species, having a shorter hinge line, only six cardinal teeth, an angular umbonal ridge, and distinctly striated post-cardinal slopes.

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