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Show 1881.] 'LIGHTNING' AND ' PORCUPINE ' EXPEDITIONS. 941 angular and has no distinct rostrum; but it may have been the ancestor of the recent species. 12. NE^ERA CONTRACTA1, Jeffreys. (Plate LXXI. fig. 4.) S H E L L transversely oblong, convex, thin, opaque, lustreless: sculpture, 25-30 riblets or raised strise in the line of growth, those on the rostrum being at a right angle to the rest: the rostrum is sometimes angulated and keeled : colour whitish : margins rounded on the anterior side, contracted and gently curved in front, whence there is a gradual slope to the snout-like rostrum; posterior side having a truncated extremity ; dorsal margin somewhat incurved : Beaks small, blunt, intorted and sunken ; umbones prominent: cartilage-pit narrow, oblique : hinge-line slightly curved on the anterior and nearly straight on the posterior side : hinge-plate reflected anteriorly, and somewhat thickened posteriorly: teeth, a single slight laminar lateral on the posterior side of the right valve, parallel with the hinge-plate, and extending to the upper end of the rostrum : inside glossy : muscular scars large and distinct. L. 0*2, B. 0*35. 'Porcupine' Exp. 1870: Atl. St. 16, 17, 17a. Several valves. Easily distinguishable from N. lamellosa, not merely by its greater size, but by its narrow or contracted shape and proportionally large rostrum ; the lateral tooth also, in N. lamellosa, is triangular and short, not laminar and elongated as in the present species. Another species, from the ' Challenger' Expedition, has been named coarctala {coartata) by Mr. Watson. 13. NE^RA SEMISTRIGOSA2, Jeffreys. (Plate LXXI. fig. 5.) S H E L L oval-oblong, convex, thin, semitransparent, and rather glossy : sculpture, 12-15 delicate concentric riblets on the posterior side only; the rostrum is closely wrinkled across ; and the rest of the shell is smooth : colour clear white: margins rounded, somewhat wedge-shaped on the anterior side, gently convex in front, and sloping upwards to the posterior side ; rostrum slightly upturned, short and broad, defined by a shallow indentation, with a truncated extremity ; dorsal margin interrupted by the umbo, raised on the anterior, and nearly straight on the other side: Beaks sunken, small, and mamillar; umbones prominent : cartilage-pit pear-shaped, lying obliquely under the beak: hinge-line corresponding with the dorsal margin : hinge-plate thin, reflected on the anterior side .* teeth, a long laminar lateral on each side of the right valve, that on the posterior side being triangular in the middle : inside polished : muscular scars triangular and large. L. 0*25, B. 0*4. 'Porcupine' Exp. 1870: Atl. St. 16, 17, 17a. Allied to N. notabilis ; but the shape of the present species is more oval or oblong, the concentric ridges are less numerous and are confined to the posterior side, the rostrum is broader and not keeled and is separated by a shallow indentation, and the lateral teeth are much larger. 1 Contracted. - Half-wrinkled. |