Three Fossil Mollusca from the Hokonui System (Triassic and Jurassic)
[Received by the Editor, February 11, 1955.]
The Mid-Trias fossil identified by O. Wilckens as Pseudomonotis? sp. indet. is redescribed, figured and named. The previous missing holoytpe of the Upper Jurassic Aulacosphinctoides sisyphi (Hector) is figured. The species was based, previously only on a crude wood-cut. Belemnite hooks from the Upper Jurassic of Kawhia arc described and named.
“Chlamys” kakanuia Marwick n.sp. Fig. 1.
1927. Pseudomonotis? sp. indet. Wilckens, N.Z. Geol. Surv. Pal. Bull. 12: 37, Pl. 8, Fig. 3.
Shell of moderate size, inequilateral, obliquely suboval, little inflated; umbo not rising above dorsal margin. Sculpture of about 30 very low axial ribs, broad and with linear interstices over much of the disc, but anterior and posterior ones narrowly ridged and separated by wide interspaces; concentric ridges poorly developed. Ears fairly large, confluent with disc, bearing numerous, regularly spaced, extremely fine lamellae, those on the larger ear crossed by still finer radial threads.
Holotype. N.Z. Geological Survey.
Dimensions: Height, 17 mm; length, 16 mm; inflation, 1 mm.
Locality. Mt. St. Mary, Kakanui Range, North Otago.
Stage. Kaihikuan (about Ladinian).
This fossil, known only from the single-valved holotype, was accidentally omitted from the writer's revision of the Hokonui faunas (N.Z. Geol. Surv. Pal. Bull. 21). It is an internal mould on which, as commonly happens, a good deal of the external sculpture has been impressed, particularly that of the ears. Wilckens stated that the ears are not preserved in full outline, and this is true of the exact detail of the dorsal margins; but in an oblique light, the lateral margins of both are clear, as also are numerous, very fine lamellae indicating earlier outlines. These show, beyond doubt, that the shell is not the right valve of Pseudomonotis or of Claraia, or indeed of any genus with a byssal notch in that valve.
The shell, on first sight, seems to have the umbo inclined to the right and therefore to be a right valve. This is due to the broadly rounded right margin of the disc with its short dorsal slope to the umbo, compared with the longer and steeper dorsal slope to the more narrowly rounded left margin. The ears, however, by their relative size and shape, suggest rather the left valve of a shell akin to Chlamys, but differing in that the umbo is well behind the middle and the ears merge gradually with the disc, without any dividing groove.
Although compression has been severe in the Mt. St. Mary beds, the characters described seem not to be the result of this, because the fine lamellae of the ears, the regular outline of the disc, and the course of the radials show no signs of distortion.
Comparable species appear to be the Bosnian upper Triassic Pecten (? Entolium) pervulgatus Bittner (1903, Jb. geol. Reichsanst. (Bundesanst.), Wien 52 (3 & 4): 609, Pl. 26, Fig. 25) and the upper Carboniferous Aviculopecten sp. indet. of Diener (1899, Palaeont. indica, ser. 15, 1 (2): 16, Pl. 1, Fig. 3).
These shells may represent an early, as yet unnamed division of the Pectinidae allied to Chlamys; but until both valves are known we cannot be certain.
1886. Ammonites sisyphi Hect. Outline of N.Z. Geol.: 68, Fig. 33, No. 1 (figure only).
1923. ?Aulacosphinctoides sisyphi (Hect.); Spath, Quart. J. Geol Soc. 79 (3): 299.
1927. Perisphinctes sp. Boehm, 1911; Wilckens, N.Z. Geol. Surv. Pal. Bull. 12. 52.
1953. Aulacosphinctoides sisyphi (Hect.), Marwick, N.Z. Geol. Surv. Pal. Bull. 21: 120.
The holotype, through the kindness of Mr. G. C. Shaw, of Dominion Museum, has been found, and is now in the Geological Survey Collections. It has had a maximum diameter of about 375 mm, and is securely attached by the concretionary mudstone matrix to a large piece of silicified wood. The specific name refers to the consequent resemblance to a small boy's toy of ancient design, consisting of a wheel or disc fixed on an axle at the end of a long stick for a handle, and run along the ground as a hoop; hence the “rolling stone” of Sisyphus. A tradition at the Geological Survey is to the effect that Hector here perpetrated an obscure pun on the name of the Honourable W. Rolleston, of Christchurch, who had in some way been concerned with the fossil.*
Laterally compressed, curved, hollow hooks or spines, with widely bifurcate root above which they may be slightly constricted, even twisted, from here gradually expanding for about half total length, then tapering to a fine point. The outer surface bears numerous low, elongate tubercles and tubercular ridges, tending to diverge from the medial line, rather stronger marginally. The material forming the outer shell is a black, jet-like substance with conchoidal fracture. The brownish matrix of the interior mould has a very low medial ridge, rather nearer the inner than the outer edge, with faint, irregular rays extending
[Footnote] * The tradition has now been confirmed by Dr. C. A. Fleming with the following references: 1886. 20th Ann. Rep. Col. Mus. Lab: 22. 1887. 22nd Ann. Rep. Col. Mus. Lab.: 35.
obliquely forward on each side and evidently corresponding to the ridges and tubercles of the surface.
Holotype. N.Z. Geological Survey, collected by K. J. McNaught, Soil Research Station, Rukuhia.
Three paratypes in the Auckland University Geology Department Collections were kindly lent for this record by Dr. C. R. Laws. They show the external sculpture, very clearly, but their “roots” are missing.
Dimensions. Holotype: length, 22 mm; maximum depth, 2.4 mm; maximum curvature, 8 mm.
Paratype: length (incomplete), 20 mm, perhaps 28 mm complete; maximum depth, 4 mm.
Locality. Puti Point, Kawhia Harbour.
Stage. Ohauan (about Tithonian).
D. T. Donovan (1953, Medd. Grnland. 111 (4): 76) describing upper Jurassic fossils from East Greenland stated that Onychites “has been used for the hooks which were borne on the arms of certain dibranchiate cephalopods, and also for somewhat similar, usually much larger, objects of unknown origin. Small ‘Onychites’ are well known and are sometimes found associated with fossil belemnoids in their original positions, arranged in two rows along each arm. The hooks are usually less than 5 mm long and are often of almost microscopic size.”
The holotype of Onychites macnaughti while agreeing in a general way with Donovan's larger specimens, differs in having a bifurcate root instead of one with a flat base, in having a tuberculate surface, and in being rather less strongly curved. Donovan concluded that “the large ‘Onychites’ must have belonged to an animal of much greater size than was normal among belemnoids” and that “Since no other hard parts have been described which could have belonged to such an animal, it presumably had no skeletal elements apart from the hooks.”
G. C. Crick (1907, Proc. malac. Soc. Lond. 7.: 269, Pl. 23) has figured specimens of English Liassic belemnites showing the double rows of hooks with expanded bases that furnished each of the six arms. Many of these hooks are five millimetres long, and so one-eighth to one-tenth as long as the arms. On the same proportions, the animal of the Puti specimen would have had arms about 20 centimetres long, and, judged by current reconstructions of belemnites, a total length of perhaps a metre. At Puti Point, guards up to ten centimetres long and phragmacones of four or five centimetres diameter are comparatively common (Belemnopsis brownei (Marshall)), and it seems not impossible that the animal of these could have been a metre long. On the other hand, these large hooks may represent such animals as the Recent squids Onychoteuthis and Ancistroteuthis which have somewhat similar armature at the end of their two long tentacular arms. Further evidence is needed before the exact systematic position of the Puti Onychites can be determined.
Dr. J. Marwick70 Cambridge Terrace