Stromboidea

• Rostellariidae
  • Rostellariella
    • Rostellariella sumatrensis (Wissema, 1947)

Original Description of Tibia (Rostellariella) sumatrensis by Wissema, 1947, p. 89:

• "Shell large, thin, conical, with convex whorls. Nuclear whorls smooth, rounded, not separated from the spire. On the older whorls occur indistinct axial depressions, looking somewhat like lines of growth, which on the younger whorls are not visible any through the spiral sculpture. On the third whorl a spiral groove comes into being close to the forward suture. Gradually more spirals are added beginning in front. On the sixth whorl the whole surface of the whorl is covered by 13 flat spirals, separated by equal grooves. The suture is rather shallow, because the whorls are little depressed behind. The two hindmost spirals are narrower than the others. The grooves are packed with fine axial filae, which form concave lines. On the penultimate whorl the foremost spiral is covered by the last whorl, so that there remain only 12 spirals. After the varix on this whorl there is added however a spiral behind; while between the three foremost spirals a secondary one is present. The base of the ultimate whorl is decorated in the same way as the spire. Twenty-three spirals are present, which are narrower and get more so towards the front while at last, near and on the canal they are reduced to mere lines. The interspiral axial filae become weaker too forward, to fade away before the canal is reached. On the ultimate whorl a broad, rounded, not very prominent varix is present, with a shallow depression in front. Here a fine line indicates the edge of the aperture, which was only very little curved forward below the middle, while it was curved inward at the beginning of the canal. Two more varices occur, one on eachof the preceding whorls. As no adult specimens are present, little can be said of the aperture. It will have been rather narrow ovate, and the canal a little twisted in front.

Locus typicus: Loc. 108, Nias Island, North Sumatra, Indonesia

Holotype Sizes: High 71.0 mm, Diam. 20.8 mm.

Tibia (Rostellariella) sumatrensis Wissema, 1947; Holotype; pl. 4, fig. 107, 108

Comment Wissema, 1947, p. 90:

• "The description has been made after the holotype. In addition can be said, that sometimes there are 11 spirals instead of 12. This beautiful species is related to. T. delicatula (Nevill), but easily distinguished by its strong sculpture on the whole shell except the very oldest whorls. Moreover the whorls are more convex and lack the distinct flat depression in front of the suture T. martinii (Marrat), a very rare species from the Philippines, is also related, but it is bisulcate near the suture, while the whorls are narrower, and its apex more acute. The holotype is still a juvenile specimen and for the rest only fragments of the topwhorls, mostly with the protoconch, were collected. In spite of this I did not hesitate to place it under Rostellariella, as it has all the characteristics of this group, and moreover is closely related to the type of this subgenus."

References

• Wissema, G.G. 1947, Young Tertiary and Quaternary Gastropoda from the Island of Nias, - Leiden. 1-212, pls. 1-6. Thesis.