Art. LII.—Two New Fossil Mollusca.
[Read before the Otago Institute, 4th October, 1910.]
Plates XXX, XXXI.
1. A New Fossil Turritella.
Turritella semiconcava n. sp. Plate XXX.
Shell large, high and narrow, many-whorled, with 8 to 10 cinguli on the lower, slightly concave whorls, and a deep suture towards the base. Sculpture. The first few post-nuclear whorls have 4 equidistant spiral cords, the third much stronger than the others (fig. 1b); the following whorls have 5 subequidistant cinguli; gradually the number of cords increases on the whorls, the body-whorl of an adult specimen having usually 10 cords; the same sculpture is continued upon the base. Spire high, narrowly conic. Protoconch not seen. Whorls about 18 to 20 on a fullgrown specimen, slowly and regularly increasing, flat on the upper whorls, lightly concave further down; the body-whorl narrowly rounded towards the flattish base. Suture on the upper part of the shell not much impressed, but gradually getting deeper approaching the base. Aperture subquadrate. Outer lip with a moderate broadly rounded sinus.
An adult specimen would have a diameter of 18–19 mm., and a height of about 95 mm; angle of spire, 11°.
Loc.—Mitchell's Point, Kaitangata Beach, Otago (Professor J. Park).
Professor James Park most kindly sent me specimens of this new Turritella for description, accompanied by the following remarks: “It occurs in thousands in thin calcareous tabular and lens-shaped masses in a greenish sandstone. Its associates are Conchothyra parasitica, Chenopus sp., Belemnites lindsayi, and many other forms. The Upper Kaitangata coal-bearing series are assigned to Upper Cretaceous.”
Type in my collection.
Remark.—In sculpture this species is nearest to T. cavershamensis Harris (= gigantea Hutton), and in the concavity of the lower whorls it approaches T. concava Hutton, but it is decidedly distinct from both.
The photo reproduced on the plate was taken by Mr. A. G. Macdonald, and kindly sent to me by Professor Park.
2. A New Fossil Mactra.
Mactra chrydaea n. sp. Plate XXXI.
Shell small, ovate-trigonal, somewhat inflated, not gaping, with rather coarse concentric sculpture, equivalve, somewhat inequilateral, the anterior end a little shorter. Beaks slightly anterior, close together, prosogyrate, incurved, pointed. Anterior end convex, the dorsal margin lightly rounded, oblique. Posterior end subtruncated, very little arched, the dorsal margin convex and rather rapidly descending. Basal margin lightly convex, forming an obtuse angle with the posterior margin. Posterior area but ill defined, an obtuse keel descending from the beak to the postero-ventral angle. Sculpture consisting of well-marked concentric ridges, usually with deep sulci towards the base; under a lens rather distant radiate striae can be seen, which are more distinct on the median part of the valves.
None of my specimens shows the interior of the valves, and the matrix is too hard to be removed without breaking the valves.
Length, 23 mm.; height, 19 mm.; diameter, 15 mm. (specimen figured). Length, 28 mm.; height, 22 mm.; diameter, 19 mm. (larger shell).
Type in my collection.
Loc.—It occurs in great abundance in the upper horizon of the Lower Pliocene blue sandy clays on the North Island Trunk Line, between Mataroa and Turanga-a-rere (J. Park).
Remarks.—This species is quite distinct from all the Recent and fossil New Zealand species of the genus. I wish to thank Professor J. Park for the specimens and the opportunity of describing them. The photo was most kindly provided by Mr. A. Hamilton, Director of the Dominion Museum.