Art. LXXVI.—On the Belemnites found in New Zealand.
Plates XXII., XXIII.
[Read before, the Wellington Philosophical Society, 12th January, 1878.]
Notwithstanding that our knowledge of the true nature and function in the animal economy of the singular fossils comprised in the group Belemnitidœ is very imperfect, their importance as indicating particular zones in the life-development of successive epochs has been fully recognized. That they were the internal supports of soft-bodied molluscs allied to the Sepia of the present day is certain, but there is no organ strictly analogous to them to be found in the structure of any living form of cephalopod. We are therefore ignorant of the extent to which the variations in form in the fossil belemnites were dependent on or correlated with important modifications in the structure of the complete animal. Nevertheless these varieties are very constant and characteristic of the particular geological formations in which they are found, so that they afford most valuable indications to the stratigraphist.
The Belemnitidœ first appear in the liassic period, and survive to the close of the cretaceous period. They are divided into two genera—Belemnitella, which is confined to the chalk or upper cretaceous formations, and Belemnites, which, with the exception of a single species (in England at least), is confined to the formations below the chalk.
No representative of Belemnitella, which is distinguished by a ventral fissure of the guard and external vascular impressions, has yet been discovered in New Zealand, so that in the following notes attention is confined to the genus Belemnites.
In order to facilitate the comparison of our belemnites with those described from other countries I reproduce the grouping of the species adopted by Phillips, Mayer, and other writers on the subject, modifying it to comprise the New Zealand forms.
1. Acœli.—Club-shaped and laterally compressed, without dorsal or ventral grooves, but with lateral furrows. (Liassic.)
2. Gastrocœli.—Cylindrical with a distinct ventral groove. (Jurassic.)
3. Notocœli.—a. Notosiphiti: Fusiform, with a dorsal groove, siphuncle on dorsal aspect, and lateral furrows. b. Gastrosiphiti: Subcylindrical, with siphuncle on ventral aspect, and short lateral grooves. (Lower Cretaceous.)
Unless it be by certain forms in the liassic strata of the Hokanui and Kaihiku ranges of Southland of which only the large phragmacones have been preserved, the first of these groups has no species in New Zealand representing the Clavati of Europe.
In the second group, which includes the sub-groups Canaliculati and Hastati, there are seyeral species found in the Putataka formation, both in the North and South Islands.
The great majority of forms found in New Zealand belong to the third group, but only to its second section, the first section, representing the Dilatati of the European neocomian formations, not being present in our collection. They are very common in the Amuri series, which is equivalent to the lower greensand, and is remarkably rich in belemnites in a perfect state of preservation, but they also survive to the horizon of the upper greensand.
The New Zealand forms of this subdivision are characterized by the absence of any ventral or dorsal grooves, by a variable form—being cylindrical, hastate, or depressed—by the constant presence of short lateral grooves on the upper part of the guard, and the ventral position of the siphuncle that traverses the septa of the phragmacone.
There are five well-marked varieties that might be considered as specifically distinct were they not so intermixed in the same strata. I have referred these to M. Duval-Joave's subdivision Gastrosiphiti of the neocomian belemnites, on account of the position of the siphuncle, which is probably of more anatomical significance than the grooves on the external surface of the guard; but in the European species a dorsal groove is always present, whereas it is absent in all the belemnites I would associate in this group from the lower cretaceous formations of India, Australia, and New Zealand.
1. Belemnites otapiriensis, sp. nov.
PI. XXII., fig 1.
Guard unknown, being only represented by a crushed mass having a longitudinal fibrous structure. Phragmacone with from twenty to thirty septa, slightly elliptical in form, outline forming an angle of 15°. Siphuncle marginal on the major transverse axis, the septa being inserted round the aperture so as to form almost a continuous tube traversing the septa.
This belemnite ranges through the Otapiri series (liassic) down close to the horizon of the Monotis beds of the Wairoa series (triassic), and though
it is not actually found with Monotis, it is associated with fossils that are also common to the lower triassic formation. It is near to B. elongatus of the lias of Britain.
2. Belemnites aucklandicus, Hauer, Novara Exp., Geol., II., 29.
PI. XXII., fig. 2, a, b.
According to Dr. Waagen this is very nearly the same as B. kuntkotensis of the lower jurassic formations of Kutch,* and, according to Professor Taite, is hardly distinguishable from B. sulcatus of the lower oolite of Great Britain.†
Occurs in dark-coloured marly sandstones of the Putataka series, Waikato South Head, and also in similar strata in the Hokanui Range, Southland. In the latter case it occurs in the upper part of the Putataka series, associated with Trigonia costata and other middle jurassic fossils.
3. Belemnites catlinensis, sp. nov.
Pl. XXII., fig. 3, a, b.
Guard slender, sub-hastate from being constricted below the alveolus, and widest at the distal third of its length, where the diameter is onetwelfth of the total length and half the length of the alveolus. Phragmacone acute, forming an angle of 18°, with about 16 septa, eccentric, the apex being nearer to the ventral margin. A wide groove extends along the ventral surface from over the alveolus, but disappears short of the apex. In section the guard is slightly compressed. Total length of largest specimen, six inches.
In dark-coloured argillaceous sandstones, south of Catlin River, Otago, and in the Hokanui Range, where it is associated with Ammonites novœ-zealandiœ.
This species is very near to B. fusiformis of the lower oolite of Britain, and to B. gerardi of India; ‡ but if faint lateral vascular markings are to be considered as true furrows, as in that species, both this species and B. aucklandicus must be classed with the group Hastati, in which case no representative of the Canaliculati has yet been found in New Zealand.
4. Belemnites hochstetteri, sp. nov.
(?) B. aucklandicus, var. minor, Hauer, Novara Exp., Geol., II.
Pl. XXII., fig. 4, a, b.
Guard symmetrical, cylindrical, short, with a sharp conical apex. Diameter of guard one-eighth of the total length. Alveolus about one-
[Footnote] * Palæon. Indic., 1873, p. 4.
[Footnote] † Q. J. Geol. Soc., XXII., pl. 7.
[Footnote] ‡ Waagen, Pal. Ind., 1873, p. 13.
fourth of the total length. Ventral surface of guard with a broad shallow groove continued almost to the apex, and with distinct lateral furrows on the lower third.
This species is easily recognized from B. aucklandicus by the straight central axis of the guard (which is also more slender), the tapering apex, and the well-marked lateral furrows which are discernible in perfect specimens.
From grey calcareous marls with Inoceramus haastii that overlie the plant-beds of the Mataura series, Kawhia Harbour, and East Cape district of the North Island. Upper Jurassic.
PI. XXIII., αε.
5. Belemnites australis, Phillips, Q. J. Geol. Soc., XXXVI., 259.
Belemnites lindsayi, Hector, N.Z. Geol. Rep., 1873–4, xiii.
Deep furrows on the dorsal angles of the lateral areas of the anterior portion of the guard extending only slightly beyond the depth of the alveolar cavity. Angle of the phragmacone from 20° to 30°.
Guard sub-hastate, depressed, trigonal anteriorly, oval in section of middle portion, and terminating in a blunt conical point, sometimes tuberculate at the apex. Length of guard twice that of the phragmacone.
Occurs in the calcareous greensands of the Amuri series at Amuri Bluff and Cape Campbell, and in the upper greensands overlying the brown coal at Waipara, Green Island, Waitaki, and Mount Hamilton.
There is no doubt, I think, that this belemnite is the same species as that described by the late Professor Phillips as a fossil from Queensland, but without any distinct locality or stratigraphical position being assigned to it.
It is probably also identical with B. seclusus, Blandford, from the Ootadoor group of the cretaceous formation of India.*
While this species maintains the above general characters with great constancy, the large series of specimens which I am able to exhibit, upwards of sixty in number, show a wonderful variety in the form and proportions of the guard, even in specimens of similar size. Five distinct forms may be described.
Var. αa.—Lateral furrows short, deep, and straight. Angle of phragmacone 32°. Guard slightly hastate, with a blunt apex. Alveolar cavity nearly half the length of the guard.
Var. β.—Lateral furrows long, shallow, and sinuous. Angle of the phragmacone 28°. Guard fusiform, depressed on dorsal surface. Apex
[Footnote] * Pal. Ind., 1861, p. 5.
rounded and perforate. Alveolar cavity one-fourth the total length of the guard.
Vay. γ.—Lateral furrows long and deep, and curved to the dorsal aspect. The length of the guard is five times that of the fifteen septa in the phragmacone. The form of the guard is hastate, owing to the expansion of the alveolar walls and the tapering of the apex.
Var. δ.—Guard sub-cylindrical, and constricted at the alveolus. Lateral furrows short, and suddenly reflected to the dorsal aspect. Apex blunt, with a terminal tubercle or knob. Length of alveolus one-fourth that of guard.
Var. ε.—Lateral furrows short, deep, and bent towards the ventral aspect. Guard depressed on both dorsal and ventral surfaces. Apex subconical. Angle of the phragmacone 25°. Septa very close, numbering 25–30.
The series of sections exhibited illustrate the structure of this belemnite, and especially display the mode in which the central portion of the guard frequently exfoliates, casting from its interior a smooth fusiform body, produced and slightly laminated in structure at the upper end, and blunt with a minute depression or perforation at the lower end. These form the Acanthocomax of Miller, and have frequently been mistaken for spines of Cedaris. They are not formed, as has been suggested, by the abrasion or weathering of the guard of the belemnite, but are due to its structural arrangement, which, notwithstanding the appearance of radiating prisms in the interior, really consists of concentric laminæ arranged in fusiform layers round the central axis. In some of the specimens the axis is seen to be an open canal filled with the sand of the imbedding matrix. This canal seems to be continuous with the siphuncle that traverses the septa of the phragmacone, and to perforate or be a continuation of the conotheca, passing on one side of the spherical pellet or nucleus that forms the apex of the phragmacone.
None of the varieties into which I have sub-divided Belemnites australis can be considered to have a peculiar horizon or stratigraphical distribution. The lower greensand in the Amuri section has been divided as follows in descending order:—
Black grit or car-stone.
Aporrhais ornata beds.
Trigonia sulcata beds.
Belemnites first appear in the calcareous conglomerate, and constitute the whole mass of the belemnite beds, almost to the exclusion of other fossil forms, but they continue plentiful up to the black grit, in which they become scarce.
The next bed above the black grit is the boulder sand or saurian bed, and in this no belemnites have been found; but they again appear in the concretionary greensands, but are there represented only by the peculiar forms which I have shown to result from the exfoliation of the perfect guards, and no trace of a belemnite possessing the upper part of its guard or phragmacone has been discovered in any bed above the black grit. This disappearance of the perfect belemnites in the upper greensand strata may be, I think, accounted for by the gradual change in the nature of the matrix, and the accession of the same unfavourable circumstances which led to the extinction of the race.
Explanation of Plates.
Fig. 1. Belemnites otapiriensis, sp. nov.
Fig. 2. Belemnites aucklandicus, Hauer.
a. ventral, b. lateral aspect.
Fig. 3. Belemnites catlinensis, sp. nov.
a. lateral, b. ventral aspect.
Fig. 4. Belemnites hochstetteri, sp. nov.
a. lateral, b. ventral aspect.
Belemnites australis, Phillips.
Var. α. a′. dorsal, a″. lateral aspect.
a′″. longitudinal section.
s′. transverse section of phragmacone.
s″. do. of guard.
Var. β. b′. lateral aspect, b″. longitudinal section.
s′. transverse section of phragmacone.
s″. do. of guard.
Var. γ. c′ ventral, c″. lateral aspect.
c′″. longitudinal section of alveolus.
Var. δ. d′. ventral aspect, d″. longitudinal section, showing exfoliation of the central core, d′″. lateral aspect.
s′. transverse section of guard.
s″. do. of phragmacone.
Var. ε. e′. dorsal, e″. lateral aspect.
e′″. dorsal, e″″. lateral. aspect, juv.
s′. transverse section of guard.
δ″. do. of phragmacone, juv.