Propeamussium cancellatum (E. A. Smith, 1885)
SMITH, E. A. 1885. Report on the Lamellibranchiata collected by H.M.S. Challenger during the years 1873-76. In C. W. Thomson & J. Murray: Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-1876. Zoology, 13: 1-341, pls. 1-25 [p. 315, pl. 23, figs. 8-8c]
1885 Amussium [sic] cancellatum E. A. Smith, 1885
E. A. Smith, 1885, plate 23.
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«Testa compressa, parum pellucida, albida, hand polita, sequilateralis, rotundata, paulo inaequivalvis, valvis diverse sculptis. Valva dextra profundior, liris tenuissimis radiantibus numerosis aliisque gracilioribus confertioribus concinne cancellata, sinistra concentrice sulcata, sulcis regularibus, tenuibus, sensim accrescentibus. Auriculae inaequales, posticis majoribus. Umbones acuti, lateribus convergentibus leviter concavis. Linea cardinis brevis, recta, fossa mediana ligamenti parva instructa. Pagina interna nitens, liris mediocriter fortibus circe 12 (aliis minoribus saepe interpositis) munita.
This species is as a rule a trifle longer from the beaks to the lower margin than from side to side. It is compressed, slightly inequivalve, only a little transparent, whitish, hardly at all glossy, and has the valves diflerently sculptured. The right or somewhat deeper valve is ornamented with numerous fine thread-like radiating lirse, which are crossed by still finer concentric ones. The former are more slender and closer together down each side than towards the middle of the valve, and the latter, besides being finer than the radiating lirse, are also much more approximated to one another, those near the beaks being further apart than the rest. The left valve has somewhat of a silky appearance, and is finely and closely concentrically lirate, the lirse gradually becoming thicker and more remote with the growth of the shell. The auricles are small, somewhat unequal, the posterior being rather larger than the anterior. They are sculptured with fine lines of growth and sometimes denticulate at the top. The posterior end of the left valve is sinuated below, and is separated from the main part of the valve by a deepish groove, in which a slender ridge runs parallel with the dorsal slope. The beaks are small, acute, the slightly concave sides converging to an angle of about 117 degrees. The glossy interior of the valves is strengthened with numerous white fairly strong radiating lirae, visible exteriorly, especially in the right valve, which is a little more transparent than the left. They are about twelve in number, somewhat thickened towards the outer extremities, which in adult shells do not reach the outer margin of the valves. Between the outer ends very short intervening ones are frequently met with, varying in number and length.
Length 16 mm., height 18, diameter 4½. Habitat.— Stations 33 and 56, off Bermuda, in 435 and 1075 fathoms; Station 24, off Culebra Island, in 390 fathoms, and off St. Thomas (depth not stated). This species is without difficulty separable from Amussium lucidum by its different sculpture, stronger substance, thicker internal liage, and different form of the auricles. The left valve is rather like that of the above-named species in respect of sculpture, but is less glossy and more strongly concentrically ridged.» EDGAR ALBERT SMITH, 1885
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