A New Fossil Cirrepede from New Zealand Miocene Beds.
[Read before the Auckland Institute, December 3, 1946; received by the Editor, January 16, 1947; issued separately, April, 1948.]
This paper marks the introduction of the genus Lepas Linnaeus to New Zealand Tertiary faunal lists. T. H. Withers, in his monograph of the New Zealand fossil cirrepedes (N.Z. Geol. Surv. Pal. Bull., No. 12, 1924), in dealing with the Lepadomorpha, discusses only the Scalpellidae, apparently at that time having no material representing the Lepadidae.
A well-preserved, intact capitulum of Lepas was recently collected by Mr. H. J. Harrington from sandstones of the Miocene at Mitimiti, north of Hokianga Harbour. The associated molluscs have been recorded in the paper immediately preceding by the present writer and the beds correlated with the sandstones at Pakaurangi Point, Kaipara Harbour.
The Lepadidae possess a capitulum that is composed of only five valves, in which respect it differs from the Scalpellidae, where the plates number more than five and the peduncle is covered with scales or plates, not naked as in the Lepadidae. Poecilasma Darwin, a related genus, differs in that the capitulum consists of a variable number of plates while the carina extends only as far as the base of the terga.
The extended distribution of modern species of Lepas is largely a consequence of their pelagic habitat, and it is reasonable to expect that similar widespread specific distribution must have obtained in the past no less than at the present day. One may therefore venture to suggest that it would be no surprise if a form specifically identical with that herein described were discovered to be present in Miocene rocks in lands distant from New Zealand. Recognising this, the writer has referred to literature relating to Australian Lepadidae, but so far no form referable to the New Zealand fossil species seems to have been recorded from the Australian region. Such, if it were to be discovered, would provide a ready means of establishing identical horizons in these two countries.
In comparing the faunas of regions that are widely separated one from the other by deep seas, identity in species whose adult habitat is confined to the continental shelf is hardly to be expected, though in rare instances organisms with a free-swimming larval stage in their life-history may have their distribution considerably extended, for their young during the larval phase of development may come to join open-sea pelagic faunas and may be distributed in like manner to these.
Discovery of the remains of a pelagic species that existed in broad seas separating remote lands may expectably provide evidence on which close correlation could be based. Unfortunately, experience shows that it is the exception rather than the rule to find the durable parts of members of an open-sea fauna preserved in deposits that have been laid down in the shallow waters of the continental shelf.
Fig. 1.—Lepas harringtoni, n.sp. Holotype, × 2.8.
Fig. 2.—Lepas anatifcra Linn. Recent, N.Z., × 1.2.
A notable exception is to be had in the case of Heligmope, a genus of the pelagic Ianthinidae, whose remains exist in both Australian and New Zealand rocks. The correlative value of this genus has been discussed by Finlay (Trans. N.Z. Inst., Vol. 62, pp. 1–6; 1931).
Preservation of the remains of pelagic organisms is typically independent of facies, and this further enhances the correlative value of such organisms, for difficulty of correlation arising from the existence of facies faunas may be dispelled by the presence of the remains of pelagic forms.
Lepas harringtoni n.sp.
The capitulum is more inflated than that of L. anatifera Linn. (Recent), and less drawn out at end remote from peduncle. Scutum notably arched outwards, its free margin also strongly arched, keeled much as in anatifera. Peduncle margin of scutum diverging from apex so as to make an obtuse angle with free margin, this angle being acute in anatifera. Tergal margin straight, almost parallel with apical end of free margin. Tergum with its apex situated at about two-thirds the length from narrow (peduncle) end, that of anatifera being almost at distal end. Anatifera has a low ridge trending from apex of tergum to distal end of free margin of scutum. This is not present in harringtoni. The carina of the fossil is much shorter, reaches less than one-half the way along tergum, and has the actual keel lightly serrated. Ornamentation of all valves is similar to that of anatifera, but the radials of the scutum are notably coarser. The coarse sculpture of harringtoni recalls that of L. pectinata Spengler, but obvious differences exist in the relative shapes and dimensions of the various elements of the capitulum.
|Capitulum||length, 18 0 mm.;||width, 12.0 mm.|
|Scutum||length, 16.5 mm.;||width, 8.5 mm.|
|Tergum||length, 12.5 mm.;||width, 5.0 mm.|
|Carina||length, 11.0 mm.;||width, 2.3 mm.|