Parvamussium obliquum (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. 313, pl. 23, figs. 6, 6a]
1885 Amussium [sic] obliquum E. A. Smith, 1885
E. A. Smith, 1885, plate 23.
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«Testa compressa, tenuissima, semipellucida, umbones versus nitens, obliqua, irregulariter rotundata. Valva sinistra inaequilateralis, liris concentricis tenuissimis instructa. Auriculae valde inaequales, postica longe majori, superne acute angulata, inferne ab valva sulco angusta profundo sejuncta. Umbo mediocriter acutus, latere obliquo postico longiore. Lirae radiantes internae circiter sedecim, quarum paucae superiores crassiores videntur.
As but a single minute and probably young left valve is all that is at present known of this species, it is with considerable hesitation that I have ventured to describe and impose a name upon it.
It is compressed, very thin, semitransparent, of an oblique growth, so that the hinder side is larger than the anterior. It is sculptured with very slender concentric lirae, which become mere striae towards the glossy umbo. This is moderately acute, the converging sides, of which the posterior is considerably the longer, meeting at an angle of about 122 degrees. The ears are very unequal, the hinder one being decidedly larger, denticulate along the top, and separated beneath from the umbonal slope by a narrow deep groove above, parallel with which is an elevated ridge bordering the auricle. It is acutely angled above and cuts in deeply below. The interior is strengthened with sixteen radiating ridges, the two uppermost (of which that on the posterior side is almost obsolete) forming the base of the ears. One or two of the upper ones on each side are very short, and appear thicker than the rest, although in reality they are not. None extend to the beak, so it is probable that very young shells are destitute of lirae. Length 3 mm., height 2¾. Habitat.— Station 24, off Culebra Island, West Indies, in 390 fathoms; Pteropod ooze. This minute valve, although without doubt very young, indicates a species of a peculiar oblique growth distinct from any as yet known.» EDGAR ALBERT SMITH, 1885
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