16. Pleurotoma (Hemipleurotoma) nodilirata, nom. mut. Plate XXII, figs. 10, 11
Pleurotoma tuberculata, T. W. Kirk, Trans. N.Z. Inst., vol. xiv, p. 409, 1882 (not of Gray); Hutton, Plioc. Moll. N.Z., in Macleay Mem. Vol., p. 50, pl. vi, fig. 29, 1893 (not of Gray).
The species, described from a Pliocene specimen, requires a new name, that proposed by Kirk being preoccupied by Gray, and the above is offered. Kirk's description being rather scanty, the following complement is now given, compiled from recent specimens.
Shell fusiform, biconical, with nodulous keeled whorls, pyriform aperture, and short open canal. Sculpture: Last whorl with about sixteen tubercles on the keel, and a similar number of spiral cords below, the upper six of which are widely spaced and narrower than the interspaces; those upon the base and canal are smaller and crowded. Above the aperture is a single chord, which persists on the whorl above, but disappears in the suture of the next whorl. Monilo-spiral threadlets adorn the sinus area, also the tubercles. All the upper whorls, except the protoconch, have tubercles on the keel, and there is a row of small nodules below the suture. The axial sculpture consists of fine rather irregular incremental lines, which, however, become more prominent on the lower whorls, connecting the small tubercles below the suture with the larger ones on the keel. Colour light-cream. Spire conical, about as long as the body-whorl. Protoconch consisting of one and a half to two whorls, nucleus obtuse, smooth, polished, the succeeding volution with minute spiral striæ. Whorls 7, slowly and regularly increasing, with a strong carina below the middle, excavated above and straight below the keel: base convex, ending in a slightly twisted rather short beak. Suture deep and margined below with a row of small elongate gemmules. Aperture pyriform, rather narrow, angular above, terminating in a short open truncated canal, which has a slight turn to the right. Outer lip sharp, strongly angled, and with a well-pronounced rounded sinus at the keel, contracted towards the base. Inner lip forming a very thin obliquely finely striated layer on the body and columella, the latter nearly straight, slightly sinuated and pointed below. Altitude, 19·6 mm.; diameter, 8·5 mm.; angle of spire, 42°.
Type of P. tuberculata, Kirk, in the Colonial Museum, Wellington.
Obs. No perfect or live specimens were gathered, only a small number of more or less damaged very fragile shells.
Of this species a smaller form occurs, but similarly sculptured,
and it seems scarcely worth a varietal name. It is also found in the Wanganui blue clay of Pliocene age. The recent specimens are imperfect in outer lip and spire, but with the aid of fossil individuals the accompanying sketch (fig. 11) is derived. The larger type specimens in the Colonial Museum are from the Petane Pliocene; in these, as also in the smaller form, the tubercles are less strong and more numerous than in recent examples.