Notes on New Zealand Mollusca. No. 5.
[Issued separately, 29th May, 1930.]
The novelty described below was lent to me by Captain Bollons several years ago. It was referred to the late Mr. C. Hedley, who stated that it was quite new to him. Some time back I had occasion to study it very closely and came to the conclusion that it was an unknown species.
The accompanying figures were drawn by Miss J. K. Allan, and are beautiful and accurate figures of a specimen which is just about the diameter of a threepenny piece. I wish to thank her heartily for her careful work. At the same time, I wish to draw a little attention to all that New Zealand conchological workers owe to the late Captain J. Bollons. He was a most untiring collector, and extremely generous with specimens and any information which he could supply. Even a casual look through the Manual of the New Zealand Mollusca will show how deeply the late Mr. Suter was indebted to him. His recent death is a great loss to New Zealand conchology, as well as to his many friends.
The following species is founded on a specimen he valued; yet, when I told him I considered it undescribed, he generously gave me his only specimen, knowing that I wished it to bear his name. Since then I came to the conclusion that it had better be placed in a new genus, and Dr. J. Marwick concurred in this opinion as neither this nor the other species dealt with in this short paper seemed to fit properly into existing genera. For the present they can remain in the Family Architectonicidae, but they differ widely from other New Zealand members of the family, and it may prove advisable to set up a new family for these depressed species.
Mangonuia n. gen.
Type Mangonuia Bollonsi n. sp.
Generic characters.—Shell small, discoidal, coiled in one plane. Apex slightly depressed. Under-surface concave, nucleus clearly visible. Whorls angular, slightly oblique, with concentric marginal threads. Aperture quadrangular. Spiral and radial sculpture. Nucleus smooth, rounded, sharply defined, slightly tilted. Another member of this genus is Omalaxis meridionalis Hedley, Australia.
Mangonuia Bollonsi n. sp. Pl. 26 Figs. 1-3.
Shell discoidal, coiled in one plane, upper surface flattened, apex very slightly depressed. Under-surface concave, widely open.
Protoconch minute, slightly tilted about 2 whorls smooth, rounded, the adult sculpture starting from a slight varix.
Whorls 4, quadrangular, the two peripheral angles granosely carinate, periphery oblique.
Sculpture, on the upper peripheral angle are two granular spiral threads, the outer much the stronger, and with five or six fine spiral striae on its under edge. On the inner edge is a single granular thread, then a tiny slope, with some spiral striae on it, to the suture. On the last half whorl the suture is clearly marked.
The whole shell is covered with extremely fine spiral striae, only visible under a strong hand-lens; they are overlaid by much stronger radial growth-lines, which are unequal in strength and spacing. On the peripheral angle are two well-marked spiral threads, one near each edge; base with a granular carina on both outer and inner edge, with a slight almost vertical drop to the suture.
Colour, pale biscuit tint.
Aperture, quadrangular externally, internally rounded. Imperfect on the holotype, about 4 mm. having been broken off.
Measurements.—Major diameter, 16.5 mm. Minor diameter, 13 mm. Height, 5 mm.
Locality.—Off North Cape, New Zealand. Depth, about 75 fms.
Material.—Holotype and one imperfect juvenile in my collection.
Remarks.—The juvenile is the specimen that on Mr. C. Hedley's identification I recorded as Discohelix meridionalis Hedley, Trans. N.Z. Inst., vol. 48, p. 125, 1915, which species is closely allied to Mangonuia Bollonsi, but has 3 peripheral threads, and the beaded row on the inner margin of both upper and under surface is more marginal than in M. Bollonsi. As stated above I consider them as congeneric. The holotype and juvenile paratype were dredged by the late Captain Bollons off the coast of Mangonui County.
Awarua n. gen.
Type Omalaxis amoena Mur. & Suter.
Suter Man. N.Z. Moll., 1913, p. 318, Pl. 15, Fig. 21, a. b.
In A Commentary on Suter's Manual of The N.Z. Mollusca, Trans. N.Z. Inst., vol. 47. p. 461, Iredale states that the genus Omalaxis must be eliminated, and transfers Omalaxis amoena M. & S. to Heliacus. Now the type of Heliacus is Solarium herberti Desh., which Tryon, in Man. Conch. (1) 9, pp. 17-18, Pl. 5, Fig. 82, makes a synonym of Torinia cylindrica Gmelin, a shell entirely different from O. amoena. It is conical, has more rounded whorls and a very different aperture. O. amoena is very depressed, has a wide, open umbilicus, with the protoconch plainly visible. I therefore name it as type of Awarua n. gen.
Generic characters.—Shell very depressed, apex flat. Protoconch minute, smooth, the extreme tip hyaline, visible from below. Whorls keeled, very slightly descending, lightly rounded; sculpture spiral and radial.
The generic name is that of the vessel from which the holotype of the genus was dredged.
Note on the operculum Awarua amoena (M. & S.).
I recently discovered in my cabinet a specimen of this species with the operculum in it. Unfortunately it is rather far down the aperture, and there are a number of sand grains adhering, but it is certainly of a conical type. Under a ⅔ objective it appears to be spirally wound, with the outer edges free. At the apex is a small pit, from which the first coil arises, passing spirally downwards.