Parvamussium squamigerum (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. 312, pl. 23, figs. 5, 5a]
1885 Amussium [sic] squamigerum E. A. Smith, 1885
E. A. Smith, 1885, plate 23.
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«Testa equilateralis, convexiuscula, rotundata, alba, subpellucida. Valva dextra concentrice laminata, lamellis tenuissimis numerosis supra porcas nonnullas radiantes obsoletas pulcherrime squamatis. Umbones parvi, acuti, Isevigati ; auriculae paulo inaequales, postico majori, incrementi lineis lamellatis radiisque obsoletis divergentibus instructi. Lirae internae undecim gracillimae, extremitatibus parum incrassatis.
This species, of which only a few right valves are at present known, is a little convex, equilateral, rounded, but rather longer from the hinge to the ventral margin than across from side to side. It is very thin, whitish, and slightly pellucid. The right valve is sculptured with numerous very fine concentric laminae, which are altogether wanting on the acute glossy beak, and towards the lower margin, in some instances, become rather more crowded than elsewhere. They have an undulating character through crossing slightly elevated radiating ridges. These vary in number according to the size of the specimen, being about fifteen in small valves, and twice that number in the largest under examination, every alternate ridge extending only about half-way from the circumference to the umbo. Upon these rays the concentric lamellae, when not worn, are elevated into vaulted scales, giving a very pretty appearance to the shell. The ears are small, somewhat unequal, the front one being rather the larger. They are ornamented with the terminations of the concentric laminae, which pass over two or three obsolete rays, more noticeable on the posterior than the anterior side. The acuteness of the beak is somewhat variable, the apical angle of divergence being 100 to 113 degrees. The internal surface is glossy, and strengthened usually with eleven radiating lirae, but at times here and there an intervening short one is met with. They are very slender, thread-like, scarcely thickened at the extremities (excepting two or three of the uppermost), and gradually disappear as they approach the umbonal region.
Length 12 mm., height 13, probable diameter 3. Habitat.— Station 24, off Culebra Island, West Indies, at a depth of 390 fathoms; also Station 33, off Bermuda, in 435 fathoms.» EDGAR ALBERT SMITH, 1885
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