Genus Zeacolpus Finlay, 1926.
Type: Turritella carlottae Hutton.

Zeacolpus chattonensis n. sp. (Figs. 47, 49.)

Shell of moderate size, apical angle about 20°. Protoconch of about two smooth whorls. Sculpture commences with two smooth spirals on first post embryonic whorl, upper spiral stronger and giving whorl strong angulation, on second whorl a weak thread appears above first two; for first three post-embryonic whorls or so, upper of the two primary spirals is stronger, but about fourth whorl the lower equals it and on fifth forms prominent keel and upper primary degenerates to fine thread. Meanwhile, fine spiral threads have been appearing from about second whorl, so whole surface is closely spiralled. Strongly-keeled condition holds for three or four whorls during which upper part of each whorl has gradually been rising above suture, forming a cingulum with two strong threads and several weak ones. One of these strong threads is probably continuation of that commencing on second whorl. The whorls which are now about 4 mm. diameter retain much the same character until about 12 mm. diameter; that is, the whorl is girdled by median concavity bounded below by single strong spiral, concave under-side of which retreats rapidly to constricted suture. Upper side of median concavity bounded by weaker spiral with another still weaker on each side, the three set on a cingulum of the whorl which retreats to suture in a convexity. Whole surface with fine spiral threads, some of which become relatively prominent. The specimen shown in figure 47 appears to be a gerontic development, the whorl is almost flat, but the suture is still well constricted. Aperture subquadrate, outer lip with a fairly deep sinus, the broadly rounded apex of which is slightly below mid whorl and posterior side advancing further than anterior.