. Bulletins of American paleontology. 312 Bulletin 180 b. C. niadhon'ia richardsi Tucker-Rowland (1938, p. 14, pi. 3, figs. 4, 5) of St Marys formation. This subspecies has 17 ribs on both valves. The concentric ornamentation near the beak shows delicate threads only in the interspaces. Further down, there are three scarcely visible radial threads on the ribs and one in the interspaces. C. richards'i Tucker-Rowland can be likened, perhaps, to C. bollenen- s'ls Mayer-Eymar (/';; Fontannes, 1880, Pliocene Vallee Rhone, p. 189) which first appears in the Miocene and characterizes the Mediterranea
. Bulletins of American paleontology. 312 Bulletin 180 b. C. niadhon'ia richardsi Tucker-Rowland (1938, p. 14, pi. 3, figs. 4, 5) of St Marys formation. This subspecies has 17 ribs on both valves. The concentric ornamentation near the beak shows delicate threads only in the interspaces. Further down, there are three scarcely visible radial threads on the ribs and one in the interspaces. C. richards'i Tucker-Rowland can be likened, perhaps, to C. bollenen- s'ls Mayer-Eymar (/';; Fontannes, 1880, Pliocene Vallee Rhone, p. 189) which first appears in the Miocene and characterizes the Mediterranean Pliocene. 2. The small and medium shells of Calvert formation. These Plum Point, Maryland, (zone 10) specimens are different from the large one of the Choptank formation, as L. Schoonover has written. They belong to the living group of Chlaiuys opera/hiris L. which corresponds to the subgenus Aequipecte)!. Comparison with C. opercidaris (Linne) from the Atlantic and its subspecies audouiui Payraudeau (in Buccjuoy, Dollfuss, and Dautzenberg, v. II, pi. 17, fig. 3-8) from the Text-fig. 6. Chlamys madisonia (Say). Young individual showing (a) auricular lamellae. Calvert fm. Resemblances—same form, d. a. p. equal to d. u. p. (see statistical table) ; lateral margins short and excavated; left valve more convex than right; same evolution of ornament near the beak—transversal striae passing over the ribs and into the spaces (Text-fig. 6) ; about 1 cm. from the beak, ribs bear a row of scales, and, further down, three rows with one row ap- pearing in the interspace. When the shells exceed 4 cm., there may be many scaly lines in the spaces and on the sides of the ribs (pi. 5, fig. 2; pi. 2, fig. 3 of Schoonover). On the interior of the left valve appear two auricular lamellae, the second disappearing late on the larger shells. The nepionic specimens of C. operculavis of the Belgian Pliocene are the same as those of young C. Please note that these imag
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