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Art. XXVI.—Some New Zealand Fossil Cephalopods.
[Read before the Otago Institute, 10th November, 1908.]
Hochstetter first discovered the remains of cephalopods in the Jurassic rocks of Kawhia. He described the species of Ammonite as A: novo-zelandicus. Two species of belemnites were also described.
In later years Hector has added several species of belemnites to those named by Hochstetter. The occurrence has been frequently recorded by Cox, McKay, and others in the rocks of the Hokonui Hills and of Kawhia. No descriptions of these have yet been written. The species here described were collected by Mr. R. Browne and the writer in the Hokonui Hills, behind Mandeville, and by Mr. Browne near Te Puti Point, in the Kawhia Harbour. The strata in the former locality have been classed as Permian or Triassic by Hector, and in the latter they have been regarded as Jurassic by all authorities.
Broncoceras mandevillei.
Diameter, 9 ½ in.; breadth, 3 ½ in.
Surface ornamented with longitudinal and transverse striæ, giving a knotted appearance to its surface. Deeply involute. Some specimens slightly constricted towards the ventral surface; others flattened. Siphuncle not discernible even in the best-preserved specimens. Siphonal lobe somewhat acute, but less so than the interior lateral lobe.
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Rather frequent in the Hokonui Hills. This appears to be the organism called in the Geological Survey reports “Palænautilus.”
Part of Suture-line of Broncoceras mandevillei.
Part of Suture-line of Arcestes hokonui.
Arcestes hokonui, n. sp.
Diameter, 2 ¾ in.; breadth, 1 ½ in.
Deeply involute, not compressed. Surface smooth, except for distant lines of growth.
Phylloceras kawhiæ, n. sp.
Diameter, 5 ½ in.; breadth, 2 in.
Deeply involute, somewhat compressed. Shell smooth, except for rather distant lines of growth. No keel.
Æ;goceras brownei, n. sp.
Diameter, 2 in.; breadth, ¾ in.
Surface marked with transverse ridges, which bifurcate near the venter. Form Anarcestes-like.
Suture-line of Phylloceras kawhiæ.
Suture-line of Æ;goceras brownci.
Orthoceras brownei, n. sp.
Diameter, 1 ½ in.; length, not known.
Septa ⅓ in. apart. Surface smooth. Siphunele not seen.
Orthoceras otapiriensis, Hector (?)
Diameter, 3 in.; length, not known.
Septa ¾ in. apart. Surface smooth. Siphunele not seen.
This organism appears to be identical with Hector's Belemnites otapiriensis, which is described as in all cases of a phragmacone without any guard. He records this form as abundant in the Hokonui Hills, the locality from which this specimen came.
It is remarkable that such genera as Broncoceras and Orthoceras should be found in strata of such late periods. The former is associated with such a curious assemblage of genera that it is extremely hard to suggest any period to which they could all belong. Among these genera are Ostræa,
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Gryphœa. Trigonia, Halobia, and Spiriferina. Since several of these are not known in strata older than the Jurassic, it is probably right to class these strata as Jurassic, thereby ignoring the presence of the archaic genera here mentioned. This conclusion seems all the more reasonable when the present isolated position of the Dominion is considered. It is quite possible that another period of isolation had terminated at the beginning of the Jurassic period. An old fauna which had lived on during the period of isolation would then be mingled with the invading newer and more vigorous types. Such an explanation might reasonably account for the rapid change in life-forms which has caused Sir James Hector to class a conformable series of rocks as of an age extending from Permian to Jurassic.